Pupillated illumination apparatus

ABSTRACT

A switchable backlight for a switchable privacy display apparatus comprises a collimated waveguide, first and second light sources and an optical turning film comprising elongate prismatic elements with facet orientations that pupillate the output of the waveguide in two orthogonal directions for each of first and second light sources. High luminance uniformity is achieved for a head-on user in privacy and public viewing modes and high uniformity of security factor is achieved for off-axis snoopers, with increased speed of privacy switch-on in privacy mode.

TECHNICAL FIELD

This disclosure generally relates to illumination from light modulationdevices, and more specifically relates to control of privacy display andhigh efficiency display.

BACKGROUND

Privacy displays provide image visibility to a primary user that istypically in an on-axis position and reduced visibility of image contentto a snooper, that is typically in an off-axis position. A privacyfunction may be provided by micro-louvre optical films that transmitsome light from a display in an on-axis direction with low luminance inoff-axis positions. However such films have high losses for head-onillumination and the micro-louvres may cause Moiré artefacts due tobeating with the pixels of the spatial light modulator. The pitch of themicro-louvre may need selection for panel resolution, increasinginventory and cost.

Switchable privacy displays may be provided by control of the off-axisoptical output.

Control may be provided by means of luminance reduction, for example bymeans of switchable backlights for a liquid crystal display (LCD)spatial light modulator. Display backlights in general employ waveguidesand edge emitting sources. Certain imaging directional backlights havethe additional capability of directing the illumination through adisplay panel into viewing windows. An imaging system maybe formedbetween multiple sources and the respective window images. One exampleof an imaging directional backlight is an optical valve that may employa folded optical system and hence may also be an example of a foldedimaging directional backlight. Light may propagate substantially withoutloss in one direction through the optical valve whilecounter-propagating light may be extracted by reflection off tiltedfacets as described in U.S. Pat. No. 9,519,153, which is incorporated byreference herein in its entirety.

In a known privacy display the privacy mode is provided by the additionof a removable louver film, such as marketed by 3M Corporation, whichmay not be reliably or easily fitted or removed by users and thereforein practice, is not assiduously attached by the user every time they areoutside the office. In another known privacy display the control ofprivacy mode is electronically activated but control is vested in theuser who must execute a keystroke to enter privacy mode.

BRIEF SUMMARY

According to a first aspect of the present disclosure, there is providedan illumination apparatus comprising: at least one light source arrangedto provide input light; a waveguide arrangement comprising at least afirst waveguide that extends across a plane and comprises: first andsecond opposed light guiding surfaces arranged to guide light along thefirst waveguide, the second light guiding surface being arranged toguide light by total internal reflection; and an input end arrangedbetween the first and second light guiding surfaces and extending in alateral direction between the first and second light guiding surfaces,the first waveguide being arranged to receive the input light from theat least one light source through the input end, and being arranged tocause light from the at least one light source to exit from the firstwaveguide through the second light guiding surface by breaking totalinternal reflection; and an optical turning film component comprising:an input surface arranged to receive the light exiting from the firstwaveguide, the input surface extending across the plane; and an outputsurface facing the input surface, wherein the input surface comprises:an array of prismatic elements each comprising a pair of facets defininga ridge therebetween, the ridges extending along an array of linesacross the plane in which the input surface extends, wherein theprismatic elements are arranged to deflect the light exiting the firstwaveguide, the deflection varying in at least one direction across theplane so that the deflected light is directed towards a common opticalwindow in front of the illumination apparatus.

The lines may be curved across the plane so that the deflection variesin a direction that is orthogonal to an optical axis that is normal tothe plane, and corresponds to the lateral direction. Advantageouslyuniformity may be increased in the lateral direction.

The facets may have respective facet angles, defined between a normal tothe facet and a normal to the plane, that may vary across the array sothat the deflection further varies in a direction orthogonal to theoptical axis, and corresponds to a direction that is orthogonal to thelateral direction, so that the deflected light may be directed towards afurther, common optical window in front of the illumination apparatus.Facet angles of respective facets, defined between a normal to the facetand a normal to the plane, may vary across the array so that thedeflection varies in a direction orthogonal to an optical axis that isnormal to the plane, the direction corresponding to a directionorthogonal to the lateral direction. Advantageously uniformity may beincreased across the illumination apparatus in the direction orthogonalto the lateral direction.

The first mentioned common optical window and the further common opticalwindow may be defined at different distances in front of theillumination apparatus. Advantageously a wider range of locations forwhich uniformity is increased is provided.

The first mentioned common optical window and the further common opticalwindow may be defined at the same distance in front of the illuminationapparatus. Advantageously the uniformity for an observer at or near theoptical window is increased.

The facets may have respective facet angles, defined between a normal tothe facet and a normal to the plane, that may vary across the array sothat the deflection varies in a direction that is orthogonal to anoptical axis normal to the plane and corresponds to a directionorthogonal to the lateral direction.

The lines of the array may have an arithmetic mean tangential angleprojected on to the plane of 0° from the lateral direction.Advantageously uniformity may be increased for an on-axis observer.

The lines of the array may have an arithmetic mean tangential angleprojected on to the plane that is inclined at more than 0° from thelateral direction. Advantageously uniformity may be increased for anoff-axis observer.

The optical turning film component may have a rectangular shape acrossthe plane and the lateral direction may be along a major or minor axisof the rectangular shape. Advantageously a rectangular shape for use inlandscape or portrait orientations may be illuminated.

The output surface may be planar. Advantageously the cost of fabricationof the optical turning film component may be reduced.

The facets may have respective facet angles, defined between a normal tothe facet and a normal to the plane may be between 40° and 70°,preferably between 42.5° and 65° and more preferably between 42.5° and62.5°. Advantageously light cones may be directed to desirable opticalwindow locations while achieving increased uniformity.

At least some of the facets may have respective facet angles, definedbetween a normal to the facet and a normal to the plane, of between52.5° and 62.5°. In respect of at least some of the facets may haverespective facet angles, defined between a normal to the facet and anormal to the plane, of between 42.5° and 52.5°. At least some of thefacets may have a respective facet angle, defined between a normal tothe facet and a normal to the plane, of between 40° and 52.5°.Advantageously displays may be provided with first and second viewinglocations with increased uniformity.

In each pair of facets, a first facet may have a normal on the internalside of the input surface that is inclined towards the input end of thefirst waveguide and a second facet has a normal on the internal side ofthe input surface that may be inclined away from the input end of thefirst waveguide, the first facets having respective facet angles,defined between the normal to the facet and a normal to the plane, thatvary across the array so that the deflection varies in a direction thatis orthogonal to an optical axis normal to the plane and corresponds toa direction orthogonal to the lateral direction.

The first facets may have respective facet angles, defined between anormal to the facet and a normal to the plane, of between 52.5° and62.5°. The second facets may have respective facet angles, definedbetween the normal to the facet and a normal to the plane, that areconstant across the array. The second facets may have respective facetangles, defined between the normal to the facet and a normal to theplane, that vary across the array. The second facets may have respectivefacet angles, defined between a normal to the facet and a normal to theplane, of between 40° and 52.5°. The first facets may have respectivefacet angles, defined between the normal to the facet and a normal tothe plane, that increase across the array with distance from the inputend, and the second facets having respective facet angles, definedbetween the normal to the facet and a normal to the plane, that decreaseacross the array with distance from the input end. The first facets mayhave respective facet angles, defined between a normal to the facet anda normal to the plane, of between 42.5° and 52.5° and the second facetshave respective facet angles, defined between a normal to the facet anda normal to the plane, of between 42.5° and 52.5°. Advantageouslyuniformity may be increased.

At least one light source may comprise an array of light sources arrayedacross the input end. Advantageously the size of the source may beincreased.

The common optical window may be aligned with an optical axis thatextends from the centre of the optical turning film component normal tothe plane. Advantageously the uniformity may be increased for an on-axisobserver.

The common optical window may be offset from an optical axis thatextends from the centre of the optical turning film component normal tothe plane. Advantageously the uniformity may be increased for anoff-axis observer.

The waveguide may further comprise a second input end arranged betweenthe first and second light guiding surfaces opposite to the firstmentioned input end, and the illumination apparatus further may compriseat least one second light source arranged to input light into thewaveguide through the second input end in an opposite direction from theat least one first mentioned light source. Advantageously first andsecond illumination profiles may be provided.

The illumination apparatus may further comprise at least one secondlight source arranged to provide input light in an opposite directionfrom the at least one first mentioned light source as viewed along theoptical axis normal to the plane; the waveguide arrangement may furthercomprise a second waveguide that extends across the same plane as thefirst waveguide and may comprise: first and second opposed light guidingsurfaces arranged to guide light along the first waveguide, the secondlight guiding surface being arranged to guide light by total internalreflection; and an input end arranged between the first and second lightguiding surfaces and extending in a lateral direction between the firstand second light guiding surfaces, the second waveguide being arrangedto receive the input light from the at least one second light sourcethrough the input end, and being arranged to cause light from the atleast one second light source to exit from the second waveguide throughthe second light guiding surface by breaking total internal reflection,and the input surface of the optical turning film component beingarranged to receive the light exiting from the first waveguide and thesecond waveguide. Advantageously uniformity may be increased.

The lines may be straight and the facets may have respective facetangles, defined between a normal to the facet and a normal to the plane,that vary across the array so that the deflection varies in a directionthat is orthogonal to the optical axis and corresponds to a directionorthogonal to the lateral direction so that the deflected light fromeach input end is directed towards respective common optical windows infront of the illumination apparatus. Advantageously the first and secondillumination profiles may provide increased brightness and uniformityacross the illumination apparatus.

The deflected light through each input end may be directed towards thesame common optical window in front of the illumination apparatus. Therespective common optical windows may be in the same location in frontof the illumination apparatus. Advantageously display brightness may beincreased. Uniformity may be further increased.

The respective common optical windows may be in different locations infront of the illumination apparatus. Advantageously multiple viewinglocations with increased uniformity may be provided.

The lines may be curved so that the deflected light input through thefirst end may be directed towards a common optical window in front ofthe illumination apparatus and the deflected light input through thesecond end may be directed towards a virtual common optical windowbehind the illumination apparatus. Advantageously uniformity may beincreased for at least one of the light sources.

The illumination apparatus further comprising a control system may bearranged to control the at least one first light source and the at leastone second light source independently. In one mode of operation thecontrol system may be arranged to provide illumination from both the atleast one first light source and the at least one second light sourcesso as to increase spatial uniformity of illumination across theillumination device for at least one viewing location. Advantageouslythe illumination apparatus may be arranged to switch between at leasttwo different illumination profiles while achieving increaseduniformity.

The waveguide may be arranged to cause light from the at least one firstlight source and the at least one second light source to exit from thewaveguide with different angular distributions. Advantageously anillumination apparatus may be arranged to provide illumination fornarrow and wider illumination profiles.

The waveguide may be arranged to cause light from the at least one firstlight source and the at least one second light source to exit from thewaveguide with a common angular distribution. Advantageously multipleoptical windows may be provided for multiple users or uniformity may befurther increased.

The illumination apparatus may comprise: at least one first light sourcearranged to provide input light; at least one second light sourcearranged to provide input light in an opposite direction from the atleast one first light source, a waveguide arrangement arranged toreceive the input light from the at least one first light source and theat least one second light source and to cause light from the at leastone first light source and the at least one second light source to exitfrom the waveguide arrangement by breaking total internal reflection,wherein the waveguide arrangement comprises at least one waveguide; andan optical turning film component comprising: an input surface arrangedto receive the light exiting from a waveguide through a light guidingsurface of the waveguide by breaking total internal reflection, theinput surface extending across the plane; and an output surface facingthe input surface, wherein the input surface comprises: an array ofprismatic elements each comprising a pair of facets defining a ridgetherebetween, the ridges extending along an array of lines across theplane in which the input surface extends, wherein the prismatic elementsare arranged to deflect the light exiting the waveguide, the deflectionvarying in at least one direction across the plane so that the deflectedlight is directed towards a common optical window in front of theillumination apparatus.

The waveguide arrangement may comprise; a waveguide extending across aplane and comprising: first and second opposed light guiding surfacesarranged to guide light along the optical waveguide, the second lightguiding surface being arranged to guide light by total internalreflection, and first and second input ends arranged between the firstand second light guiding surfaces and extending in a lateral directionbetween the first and second light guiding surfaces; wherein the atleast one first light source is arranged to input light into thewaveguide through the first input end and the at least one second lightsource is arranged to input light into the waveguide through the secondinput end, and the waveguide is arranged to cause light from the atleast one first light source and the at least one second light source toexit from the waveguide through one of the first and second lightguiding surfaces by breaking total internal reflection. Advantageouslythickness and cost may be reduced.

The waveguide arrangement may comprise: a first waveguide extendingacross a plane and comprising first and second opposed light guidingsurfaces arranged to guide light along the optical waveguide, the secondlight guiding surface being arranged to guide light by total internalreflection; and a first input end arranged between the first and secondlight guiding surfaces and extending in a lateral direction between thefirst and second light guiding surfaces; wherein the at least one firstlight source is arranged to input light into the first waveguide throughthe first input end, and the first waveguide is arranged to cause lightfrom the at least one first light source to exit from the firstwaveguide through one of the first and second light guiding surface bybreaking total internal reflection; a second waveguide extending acrossthe plane in arranged in series with the first waveguide and comprisingfirst and second opposed light guiding surfaces arranged to guide lightalong the optical waveguide, the second light guiding surface beingarranged to guide light by total internal reflection, and a second inputend arranged between the first and second light guiding surfaces andextending in a lateral direction between the first and second lightguiding surfaces; wherein the at least one second light source isarranged to input light into the second waveguide through the secondinput end, and the second waveguide is arranged to cause light from theat least one second light source to exit from the second waveguidethrough one of the first and second light guiding surfaces by breakingtotal internal reflection, and wherein the first and second waveguidesare oriented so that at least one first light source and at least onesecond light source input light into the first and second waveguides inopposite directions. Advantageously luminance uniformity may beincreased.

According to a second aspect of the present disclosure, there isprovided a backlight apparatus comprising: an illumination apparatusaccording to the first aspect; and a rear reflector arranged to receivelight exiting from the first surface of waveguide and direct it backthrough the waveguide. Advantageously efficiency of collection of lightfrom the illumination apparatus is increased.

According to a third aspect of the present disclosure, there is provideda display apparatus comprising: a backlight apparatus according to thesecond aspect; and a spatial light modulator arranged to receive lightfrom the backlight apparatus. Advantageously a display may be providedwith high uniformity for desirable viewing locations. The viewinglocations may be controlled by switching of the backlight light sources.The size of the illumination cones may be varied, to achieve switchabledisplay viewing freedom.

The display apparatus may further comprise: at least one displaypolariser arranged on a side of the spatial light modulator; anadditional polariser arranged on the same side of the spatial lightmodulator as the display polariser; and at least one polar controlretarder arranged between the display polariser and the additionalpolariser, wherein the at least one polar control retarder may include aswitchable liquid crystal retarder comprising a layer of liquid crystalmaterial. Advantageously a switchable privacy display may be providedwith a privacy mode and public mode of operation. The polar controlretarder may cooperate with a switchable backlight to achieve increasedviewing freedom in a public mode of operation. Uniformity of privacymode security factor may be increased.

According to a fourth aspect of the present disclosure, there isprovided a vehicle having a display apparatus according to the thirdaspect mounted therein. Advantageously occupants may be illuminated withhigh efficiency and may be provided with high luminance uniformity.

According to a fifth aspect of the present disclosure, there is providedan optical turning film component comprising: an input surface forreceiving light exiting from a waveguide through a light guiding surfaceof the waveguide by breaking total internal reflection, the inputsurface extending across a plane; and an output surface facing the inputsurface, wherein the input surface comprises: an array of prismaticelements each comprising a pair of facets defining a ridge therebetween,the ridges extending along an array of lines across the plane in whichthe input surface extends, wherein the prismatic elements may bearranged to deflect the light exiting the waveguide, the deflectionvarying in at least one direction across the plane so that the deflectedlight is directed towards a common optical window in front of theillumination apparatus.

According to a sixth aspect of the present disclosure, there is providedillumination apparatus comprising: a waveguide extending across a planeand comprising: first and second opposed light guiding surfaces arrangedto guide light along the optical waveguide, the second light guidingsurface being arranged to guide light by total internal reflection, andan input end arranged between the first and second light guidingsurfaces and extending in a lateral direction between the first andsecond light guiding surfaces; at least one light source arranged toinput light into the waveguide through the input end, wherein thewaveguide is arranged to cause light from the light sources to exit fromthe waveguide through the second light guiding surface by breaking totalinternal reflection; and an optical turning film component comprising:an input surface arranged to receive the light exiting from thewaveguide, the input surface extending across the plane; and an outputsurface facing the input surface, wherein the input surface comprises:an array of prismatic elements each comprising a pair of facets defininga ridge therebetween, the ridges extending along an array of linesacross the plane in which the input surface extends, wherein theprismatic elements are arranged to deflect the light exiting thewaveguide, the deflection varying in at least one direction across theplane so that the deflected light is directed towards a common opticalwindow in front of the illumination apparatus. The illuminationapparatus may provide light to a common spatial location across at leastpart of the illumination apparatus. An observer viewing the illuminationapparatus at or near the common optical window may advantageously beprovided with increased uniformity of luminance across the illuminationapparatus. An environmental illumination apparatus may provide a focusedillumination region at a desirable working distance.

Embodiments of the present disclosure may be used in a variety ofoptical systems. The embodiments may include or work with or incooperation with a variety of illuminators, environmental lighting,interior and exterior automotive illumination, projectors, projectionsystems, optical components, displays, microdisplays, computer systems,processors, self-contained projector systems, visual and/or audio-visualsystems and electrical and/or optical devices. Aspects of the presentdisclosure may be used with practically any apparatus related to opticaland electrical devices, optical systems, presentation systems or anyapparatus that may contain any type of optical system. Accordingly,embodiments of the present disclosure may be employed in opticalsystems, devices used in visual and/or optical presentations, visualperipherals and so on and in computing environments.

Before proceeding to the disclosed embodiments in detail, it should beunderstood that the disclosure is not limited in its application orcreation to the details of the particular arrangements shown, becausethe disclosure is capable of other embodiments. Moreover, aspects of thedisclosure may be set forth in different combinations and arrangementsto define embodiments unique in their own right. Also, the terminologyused herein is for the purpose of description and not of limitation.

These and other advantages and features of the present disclosure willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example in the accompanyingFIGURES, in which like reference numbers indicate similar parts, and inwhich:

FIG. 1A is a schematic diagram illustrating a front perspective view ofa switchable privacy display comprising a light pupillating turningfilm;

FIG. 1B is a schematic diagram illustrating a front perspective view ofa stack of optical components in the apparatus of FIG. 1A;

FIG. 1C is a schematic diagram illustrating a top view of a vehiclehaving the display apparatus of FIG. 1A mounted therein primarily foruse by a passenger;

FIG. 1D is a schematic diagram illustrating a top view of a vehiclehaving the display apparatus of FIG. 1A mounted therein for use by botha passenger and a driver;

FIG. 2 is a schematic diagram illustrating a front perspective view of ahigh efficiency pupillated display;

FIG. 3 is a schematic diagram illustrating a front perspective view of awaveguide for use in a pupillated display;

FIG. 4A is a schematic diagram illustrating a side view of a pupillatedbacklight for a first light source;

FIG. 4B is a schematic diagram illustrating a side view of operation ofvariable tilt facets of a turning film of a pupillated backlight for afirst light source;

FIG. 4C is a schematic diagram illustrating a rear perspective view oflight output from a pupillated linear optical turning film componentcomprising variable tilt facets;

FIG. 5A is a schematic diagram illustrating a front perspective view ofoperation of facets of a curved optical turning film component of apupillated backlight for light from a first light source;

FIG. 5B is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component comprisinguniform tilt facets;

FIG. 5C is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component comprisingvariable tilt facets with a common optical window distance;

FIG. 5D is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component comprisingvariable tilt facets with first and second different optical windowdistances;

FIG. 6A is a schematic diagram illustrating a side view of operation ofa turning film comprising variable tilt facets of a pupillatedbacklight;

FIG. 6B is a schematic diagram illustrating a top view of operation of acurved optical turning film component of a pupillated backlight;

FIG. 7 is a schematic graph illustrating the polar variation ofluminance for an illustrative backlight with light input at the firstend of the waveguide;

FIG. 8A is an array of schematic graphs illustrating the variation ofluminance for different viewing angles in a display of FIG. 1Acomprising a curved optical turning film component with variable tiltfacets;

FIG. 8B is an array of schematic graphs illustrating the variation ofluminance for different viewing angles in a display comprising a linearoptical turning film component with uniform tilt facets;

FIG. 9A is a schematic graph illustrating the polar variation oftransmission of a switchable retarder arranged between parallelpolarisers for switchable liquid crystal retarders driven for privacymode;

FIG. 9B is a schematic graph illustrating the polar variation ofrelative reflection of a switchable retarder arranged between areflective polariser and absorbing polariser for switchable liquidcrystal retarders driven for privacy mode;

FIG. 9C is a schematic graph illustrating the polar and azimuthalvariation of visual security factor, S in a privacy mode of operationfor a display head-on luminance, of value Y_(max) measured in nits thatis half of the illuminance of value I measured in lux;

FIG. 10A is an array of schematic graphs illustrating the variation ofsecurity factor, S for different viewing angles in a display of FIG. 1Acomprising a curved optical turning film component with variable tiltfacets for a display head-on luminance, of value Y_(max) measured innits that is half of the illuminance of value I measured in lux;

FIG. 10B is an array of schematic graphs illustrating the variation ofsecurity factor, S for different viewing angles in a display comprisinga linear optical turning film component with uniform tilt facets for adisplay head-on luminance, of value Y_(max) measured in nits that ishalf of the illuminance of value I measured in lux;

FIG. 11A is a schematic diagram illustrating a side view of a pupillatedbacklight for first and second light sources;

FIG. 11B is a schematic diagram illustrating a side view of operation ofvariable tilt facets of a turning film of a pupillated backlight forfirst and second light sources;

FIG. 11C is a schematic graph illustrating the polar variation ofluminance for an illustrative backlight with light input at the secondend of the waveguide;

FIG. 12A is a schematic diagram illustrating a front perspective view ofoperation of facets of a curved optical turning film component of apupillated backlight for light from first and second light sources;

FIG. 12B is a schematic diagram illustrating a top view of operation ofa curved optical turning film component of a pupillated backlight forlight from the second light source;

FIG. 13A is a schematic diagram illustrating a top view of operation ofa linear optical turning film component of a pupillated backlightcomprising variable tilt facets;

FIG. 13B is a schematic diagram illustrating a side view of operation ofa curved optical turning film component of a pupillated backlightcomprising uniform tilt facets;

FIG. 14 is a schematic diagram illustrating a rear perspective view of adiffused surface of a turning film;

FIG. 15A is a schematic diagram illustrating a side view of a pupillatedbacklight for first and second light sources;

FIG. 15B and FIG. 15C are schematic diagrams illustrating a frontperspective view of waveguides for use in a pupillated display;

FIG. 16A is a schematic diagram illustrating a side view of a pupillatedbacklight for first and second light sources;

FIG. 16B and FIG. 16C are schematic diagrams illustrating a frontperspective view of waveguides for use in a pupillated display;

FIG. 16D is a schematic graph illustrating the polar variation ofluminance for the illustrative backlight of FIGS. 16A-B with light inputinto the upper waveguide;

FIG. 17A is a schematic diagram illustrating a side view of a pupillatedbacklight for comprising first and second waveguides, each waveguidecomprising a first light source;

FIG. 17B is a schematic diagram illustrating a front perspective view ofthe pupillated backlight of FIG. 17A;

FIG. 17C is a schematic graph illustrating the variation of facet tiltsfor various optical turning film components for use with the backlightof FIGS. 17A-B;

FIG. 17D is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a first optical turning film component of FIGS. 17A-C for lightfrom the first light source;

FIG. 17E is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a first optical turning film component of FIGS. 17A-C for lightfrom the second light source;

FIG. 17F is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a first optical turning film component of FIGS. 17A-C for lightfrom the first and second light sources;

FIG. 17G is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a third optical turning film component of FIGS. 17A-C for lightfrom the first light source;

FIG. 17H is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a third optical turning film component of FIGS. 17A-C for lightfrom the second light source;

FIG. 17I is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 17A comprising the waveguide of FIG.3 and a third optical turning film component of FIGS. 17A-C for lightfrom the first and second light sources;

FIG. 18A is a schematic diagram illustrating a side view of a pupillatedbacklight for comprising first and second waveguides, each waveguidecomprising gently sloped facets and steeply sloped facets with a surfacenormal direction that is not in the plane in which the waveguideextends;

FIG. 18B is a schematic diagram illustrating a side view of a pupillatedbacklight for comprising first and second waveguides, each waveguidecomprising gently sloped facets and steeply sloped facets with a surfacenormal direction that is in the plane in which the waveguide extends;

FIG. 18C is a schematic diagram illustrating a side view of a pupillatedbacklight for comprising first and second waveguides, each waveguidecomprising a first and second light source;

FIG. 19A is a schematic diagram illustrating a side perspective view ofa turning film comprising first and second arrays of prismatic elementswherein the first array of prismatic elements comprises curved prismaticelements;

FIG. 19B is a schematic graph illustrating the polar variation ofluminance for a backlight comprising the waveguide of FIG. 3 and theoptical turning film component of FIG. 19A;

FIG. 19C is a schematic diagram illustrating a front perspective view ofa pupillated backlight comprising an optical turning film with a firstarray of prismatic elements that is linear and a second array ofprismatic elements that is curved;

FIG. 19D is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 19C comprising the waveguide of FIG.3 for light from the first light source;

FIG. 19E is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 19C comprising the waveguide of FIG.3 for light from the second light source;

FIG. 19F is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 19C comprising the waveguide of FIG.3 for light from the first and second light sources;

FIG. 20 is a schematic diagram illustrating a top view of a segmentedbacklight;

FIG. 21 is a schematic diagram illustrating atop view of a curveddisplay comprising a light pupillating turning film;

FIG. 22A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1B in a privacy mode of operation;

FIG. 22B is a schematic diagram illustrating in top view propagation ofambient illumination light through the optical stack of FIG. 1B in aprivacy mode of operation;

FIG. 23A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1B in a public mode of operation;

FIG. 23B is a schematic graph illustrating the variation of outputluminance with polar direction for the transmitted light rays in FIG.23A;

FIG. 23C is a schematic diagram illustrating in top view propagation ofambient illumination light through the optical stack of FIG. 1B in apublic mode of operation; and

FIG. 23D is a schematic graph illustrating the variation of reflectivitywith polar direction for the reflected light rays in FIG. 23C.

DETAILED DESCRIPTION

Terms related to optical retarders for the purposes of the presentdisclosure will now be described.

In a layer comprising a uniaxial birefringent material there is adirection governing the optical anisotropy whereas all directionsperpendicular to it (or at a given angle to it) have equivalentbirefringence.

The optical axis of an optical retarder refers to the direction ofpropagation of a light ray in the uniaxial birefringent material inwhich no birefringence is experienced. This is different from theoptical axis of an optical system which may for example be parallel to aline of symmetry or normal to a display surface along which a principalray propagates.

For light propagating in a direction orthogonal to the optical axis, theoptical axis is the slow axis when linearly polarized light with anelectric vector direction parallel to the slow axis travels at theslowest speed. The slow axis direction is the direction with the highestrefractive index at the design wavelength. Similarly the fast axisdirection is the direction with the lowest refractive index at thedesign wavelength.

For positive dielectric anisotropy uniaxial birefringent materials theslow axis direction is the extraordinary axis of the birefringentmaterial. For negative dielectric anisotropy uniaxial birefringentmaterials the fast axis direction is the extraordinary axis of thebirefringent material.

The terms half a wavelength and quarter a wavelength refer to theoperation of a retarder for a design wavelength λ₀ that may typically bebetween 500 nm and 570 nm. In the present illustrative embodimentsexemplary retardance values are provided for a wavelength of 550 nmunless otherwise specified.

The retarder provides a phase shift between two perpendicularpolarization components of the light wave incident thereon and ischaracterized by the amount of relative phase, Γ, that it imparts on thetwo polarization components; which is related to the birefringence Δnand the thickness d of the retarder by

Γ=2·π·Δn·d/λ ₀  eqn. 1

In eqn. 1, Δn is defined as the difference between the extraordinary andthe ordinary index of refraction, i.e.

Δn=n _(e) −n ₀  eqn. 2

For a half-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is ΓF=π.For a quarter-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is Γ=π/2.

The term half-wave retarder herein typically refers to light propagatingnormal to the retarder and normal to the spatial light modulator.

Some aspects of the propagation of light rays through a transparentretarder between a pair of polarisers will now be described.

The state of polarisation (SOP) of a light ray is described by therelative amplitude and phase shift between any two orthogonalpolarization components. Transparent retarders do not alter the relativeamplitudes of these orthogonal polarisation components but act only ontheir relative phase. Providing a net phase shift between the orthogonalpolarisation components alters the SOP whereas maintaining net relativephase preserves the SOP. In the current description, the SOP may betermed the polarisation state.

A linear SOP has a polarisation component with a non-zero amplitude andan orthogonal polarisation component which has zero amplitude.

A linear polariser transmits a unique linear SOP that has a linearpolarisation component parallel to the electric vector transmissiondirection of the linear polariser and attenuates light with a differentSOP.

Absorbing polarisers are polarisers that absorb one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of absorbing linear polarisers aredichroic polarisers.

Reflective polarisers are polarisers that reflect one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of reflective polarisers that arelinear polarisers are multilayer polymeric film stacks such as DBEF™ orAPF™ from 3M Corporation, or wire grid polarisers such as ProFlux™ fromMoxtek. Reflective linear polarisers may further comprise cholestericreflective materials and a quarter waveplate arranged in series.

A retarder arranged between a linear polariser and a parallel linearanalysing polariser that introduces no relative net phase shift providesfull transmission of the light other than residual absorption within thelinear polariser.

A retarder that provides a relative net phase shift between orthogonalpolarisation components changes the SOP and provides attenuation at theanalysing polariser.

In the present disclosure an ‘A-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisparallel to the plane of the layer.

A ‘positive A-plate’ refers to positively birefringent A-plates, i.e.A-plates with a positive Δn.

In the present disclosure a ‘C-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisperpendicular to the plane of the layer. A ‘positive C-plate’ refers topositively birefringent C-plate, i.e. a C-plate with a positive Δn. A‘negative C-plate’ refers to a negatively birefringent C-plate, i.e. aC-plate with a negative Δn.

‘O-plate’ refers to an optical retarder utilizing a layer ofbirefringent material with its optical axis having a component parallelto the plane of the layer and a component perpendicular to the plane ofthe layer. A ‘positive O-plate’ refers to positively birefringentO-plates, i.e. O-plates with a positive Δn.

Achromatic retarders maybe provided wherein the material of the retarderis provided with a retardance Δn·d that varies with wavelength λ as

Δn·d/λ=κ  eqn. 3

where κ is substantially a constant.

Examples of suitable materials include modified polycarbonates fromTeijin Films. Achromatic retarders may be provided in the presentembodiments to advantageously minimise colour changes between polarangular viewing directions which have low luminance reduction and polarangular viewing directions which have increased luminance reductions aswill be described below.

Various other terms used in the present disclosure related to retardersand to liquid crystals will now be described.

A liquid crystal cell has a retardance given by Δn·d where Δn is thebirefringence of the liquid crystal material in the liquid crystal celland d is the thickness of the liquid crystal cell, independent of thealignment of the liquid crystal material in the liquid crystal cell.

Homogeneous alignment refers to the alignment of liquid crystals inswitchable liquid crystal displays where molecules align substantiallyparallel to a substrate. Homogeneous alignment is sometimes referred toas planar alignment. Homogeneous alignment may typically be providedwith a small pre-tilt such as 2 degrees, so that the molecules at thesurfaces of the alignment layers of the liquid crystal cell are slightlyinclined as will be described below. Pretilt is arranged to minimisedegeneracies in switching of cells.

In the present disclosure, homeotropic alignment is the state in whichrod-like liquid crystalline molecules align substantiallyperpendicularly to the substrate. In discotic liquid crystalshomeotropic alignment is defined as the state in which an axis of thecolumn structure, which is formed by disc-like liquid crystallinemolecules, aligns perpendicularly to a surface. In homeotropicalignment, pretilt is the tilt angle of the molecules that are close tothe alignment layer and is typically close to 90 degrees and for examplemay be 88 degrees.

In a twisted liquid crystal layer a twisted configuration (also known asa helical structure or helix) of nematic liquid crystal molecules isprovided. The twist may be achieved by means of a non-parallel alignmentof alignment layers. Further, cholesteric dopants may be added to theliquid crystal material to break degeneracy of the twist direction(clockwise or anti-clockwise) and to further control the pitch of thetwist in the relaxed (typically undriven) state. A supertwisted liquidcrystal layer has a twist of greater than 180 degrees. A twisted nematiclayer used in spatial light modulators typically has a twist of 90degrees.

Liquid crystal molecules with positive dielectric anisotropy areswitched from a homogeneous alignment (such as an A-plate retarderorientation) to a homeotropic alignment (such as a C-plate or O-plateretarder orientation) by means of an applied electric field.

Liquid crystal molecules with negative dielectric anisotropy areswitched from a homeotropic alignment (such as a C-plate or O-plateretarder orientation) to a homogeneous alignment (such as an A-plateretarder orientation) by means of an applied electric field.

Rod-like molecules have a positive birefringence so that n_(e)>n_(o) asdescribed in eqn. 2. Discotic molecules have negative birefringence sothat n_(e)<n_(o).

Positive retarders such as A-plates, positive O-plates and positiveC-plates may typically be provided by stretched films or rod-like liquidcrystal molecules. Negative retarders such as negative C-plates may beprovided by stretched films or discotic like liquid crystal molecules.

Parallel liquid crystal cell alignment refers to the alignment directionof homogeneous alignment layers being parallel or more typicallyantiparallel. In the case of pre-tilted homeotropic alignment, thealignment layers may have components that are substantially parallel orantiparallel. Hybrid aligned liquid crystal cells may have onehomogeneous alignment layer and one homeotropic alignment layer. Twistedliquid crystal cells may be provided by alignment layers that do nothave parallel alignment, for example oriented at 90 degrees to eachother.

Transmissive spatial light modulators may further comprise retardersbetween the input display polariser and the output display polariser forexample as disclosed in U.S. Pat. No. 8,237,876, which is hereinincorporated by reference in its entirety. Such retarders (not shown)are in a different place to the passive retarders of the presentembodiments. Such retarders compensate for contrast degradations foroff-axis viewing locations, which is a different effect to the luminancereduction for off-axis viewing positions of the present embodiments.

Terms related to privacy display appearance will now be described.

A private mode of operation of a display is one in which an observersees a low contrast sensitivity such that an image is not clearlyvisible. Contrast sensitivity is a measure of the ability to discernbetween luminances of different levels in a static image. Inversecontrast sensitivity may be used as a measure of visual security, inthat a high visual security level (VSL) corresponds to low imagevisibility.

For a privacy display providing an image to an observer, visual securitymay be given as:

VSL=(Y+R)/(Y−K)  eqn. 4

where VSL is the visual security level, Y is the luminance of the whitestate of the display at a snooper viewing angle, K is the luminance ofthe black state of the display at the snooper viewing angle and R is theluminance of reflected light from the display.

Panel contrast ratio is given as:

C=Y/K  eqn. 5

For high contrast optical LCD modes, the white state transmissionremains substantially constant with viewing angle. In the contrastreducing liquid crystal modes of the present embodiments, white statetransmission typically reduces as black state transmission increasessuch that

Y+K˜P·L  eqn. 6

The visual security level may then be further given as:

$\begin{matrix}{{VSL} = \frac{\left( {C + {{I.\rho}/{\pi.\left( {C + 1} \right)}/\left( {P.L} \right)}} \right)}{\left( {C - 1} \right)}} & {{eqn}.7}\end{matrix}$

where off-axis relative luminance, P is typically defined as thepercentage of head-on luminance, L at the snooper angle and the displaymay have image contrast ratio C and the surface reflectivity is ρ.

The off-axis relative luminance, P is sometimes referred to as theprivacy level. However, such privacy level P describes relativeluminance of a display at a given polar angle compared to head-onluminance, and is not a measure of privacy appearance.

The display may be illuminated by Lambertian ambient illuminance I. Thusin a perfectly dark environment, a high contrast display has VSL ofapproximately 1.0. As ambient illuminance increases, the perceived imagecontrast degrades, VSL increases and a private image is perceived.

For typical liquid crystal displays the panel contrast C is above 100:1for almost all viewing angles, allowing the visual security level to beapproximated to:

VSL=1+I·ρ/(π·P·L)  eqn. 8

The perceptual image security may be determined from the logarithmicresponse of the eye, such that the security factor, S is given by:

S=log₁₀(V)  eqn. 9

Desirable limits for S were determined in the following manner. In afirst step a privacy display device was provided. Measurements of thevariation of privacy level, P(θ) of the display device with polarviewing angle and variation of reflectivity ρ(θ) of the display devicewith polar viewing angle were made using photopic measurement equipment.A light source such as a substantially uniform luminance light box wasarranged to provide illumination from an illuminated region that wasarranged to illuminate the privacy display device along an incidentdirection for reflection to a viewer positions at a polar angle ofgreater than 0° to the normal to the display device. The variation I(θ)of illuminance of a substantially Lambertian emitting lightbox withpolar viewing angle was determined by measuring the variation ofrecorded reflective luminance with polar viewing angle considering thevariation of reflectivity ρ(θ). The measurements of P(θ), r(θ) and I(θ)were used to determine the variation of Security Factor S(θ) with polarviewing angle along the zero elevation axis.

In a second step a series of high contrast images were provided on theprivacy display including (i) small text images with maximum font height3 mm, (ii) large text images with maximum font height 30 mm and (iii)moving images.

In a third step each observer (with eyesight correction for viewing at1000 mm where appropriate) viewed each of the images from a distance of1000 mm, and adjusted their polar angle of viewing at zero elevationuntil image invisibility was achieved for one eye from a position nearon the display at or close to the centre-line of the display. The polarlocation of the observer's eye was recorded. From the relationship S(θ),the security factor at said polar location was determined. Themeasurement was repeated for the different images, for various displayluminance Y_(max), different lightbox illuminance I(q=0), for differentbackground lighting conditions and for different observers.

From the above measurements S<1.0 provides low or no visual security,1.0≤S<1.5 provides visual security that is dependent on the contrast,spatial frequency and temporal frequency of image content, 1.5≤S<1.8provides acceptable image invisibility (that is no image contrast isobservable) for most images and most observers and S>1.8 provides fullimage invisibility, independent of image content for all observers.

In comparison to privacy displays, desirably wide-angle displays areeasily observed in standard ambient illuminance conditions. One measureof image visibility is given by the contrast sensitivity such as theMichelson contrast which is given by:

M=(I _(max) −I _(min))/(I _(max) +I _(min))  eqn. 10

and so:

M=((Y+R)−(K+R))/((Y+R)+(K+R))=(Y−K)/(Y+K+2·R)  eqn. 11

Thus the visual security level (VSL), is equivalent (but not identicalto) 1/M. In the present discussion, for a given off-axis relativeluminance, P the wide-angle image visibility, W is approximated as

W=1/VSL=1/(1+I·ρ/(π·P·L))  eqn. 12

In the present discussion the colour variation Δε of an output colour(u_(w)′+Δu′, v_(w)′+Δv′) from a desirable white point (u_(w)′, v_(w)′)may be determined by the CIELUV colour difference metric, assuming atypical display spectral illuminant and is given by:

Δε=(Δu′ ² +Δv′ ²)^(1/2)  eqn. 13

Catadioptric elements employ both refraction and reflection, which maybe total internal reflection or reflection from metallised surfaces.

The structure and operation of various directional display devices willnow be described. In this description, common elements have commonreference numerals. It is noted that the disclosure relating to anyelement applies to each device in which the same or correspondingelement is provided. Accordingly, for brevity such disclosure is notrepeated.

A switchable privacy display apparatus will now be described.

FIG. 1A is a schematic diagram illustrating a front view of a privacydisplay apparatus 200 comprising a privacy display device 100 that iscontrolled by a privacy control system 350, 352, 354. The display device100 displays an image; and FIG. 1B is a schematic diagram illustrating afront perspective view of a stack of some of the optical components inthe apparatus of FIG. 1A.

Display apparatus 100 comprises a backlight apparatus 20; and a spatiallight modulator 48 arranged to receive light from the backlightapparatus 20.

In the present disclosure, the spatial light modulator 48 may comprise aliquid crystal display comprising substrates 212, 216, and liquidcrystal layer 214 having red, green and blue pixels 220, 222, 224. Thespatial light modulator 48 has an input display polariser 210 and anoutput display polariser 218 on opposite sides thereof. The outputdisplay polariser 218 is arranged to provide high extinction ratio forlight from the pixels 220, 222, 224 of the spatial light modulator 48.Typical polarisers 210, 218 may be absorbing polarisers such as dichroicpolarisers.

Optionally a reflective polariser 208 may be provided between the inputdisplay polariser 210 and backlight 20 to provide recirculated light andincrease display efficiency. Advantageously efficiency may be increased.

The backlight apparatus 20 comprises a rear reflector 3; and anillumination apparatus 110. The illumination apparatus comprises awaveguide arrangement comprising waveguide 1, and optical turning filmcomponent 50 and arranged to receive light exiting from the firstsurface of waveguide 1 and direct it back through the waveguide 1.

The waveguide 1 further comprises a second input end 4 arranged betweenthe first and second light guiding surfaces 6, 8 opposite to the firstmentioned input end 2, and the illumination apparatus 110 furthercomprises at least one second light source 17 arranged to input lightinto the waveguide 1 through the second input end 4. In furtherembodiments described hereinbelow the second light source 17 may beomitted. Advantageously cost and bezel width may be reduced.

Optical stack 5 may comprise diffusers, optical turning film componentsand other known optical backlight structures. Asymmetric diffusers, thatmay comprise asymmetric surface relief features for example, may beprovided in the optical stack 5 with increased diffusion in theelevation direction in comparison to the lateral direction may beprovided. Advantageously image uniformity may be increased.

Display apparatus 100 further comprises: at least one display polariserthat is the output polariser 218 arranged on a side of the spatial lightmodulator 48 that in FIG. 1A is the output side. Alternatively thedisplay polariser may be the input polariser 210 arranged on a side ofthe spatial light modulator 48 that is the input side. Additionalpolariser 318 is arranged on the same side of the spatial lightmodulator 48 as the display polariser 218. Polarisers 210, 218, 318 maybe absorbing dichroic polarisers.

The display polariser 218 and the additional polariser 318 have electricvector transmission directions 219, 319 that are parallel, andorthogonal to the input polariser 210 transmission direction 211.Reflective polariser 302 further has a polarisation transmissiondirection 303 that is aligned parallel to the polarisation transmissiondirections 219, 319.

In FIG. 1A, additional polariser 318 is arranged on the same side of thespatial light modulator 48 as the display output polariser 218.Alternatively (not shown) the additional polariser 318 maybe arranged onthe same side as the input polariser 210 and polar control retarder 300may be arranged between additional polariser 318 and input polariser210. Alternatively (not shown) plural polar control retarders and pluraladditional polarisers may be provided on the input side of the spatiallight modulator 48. Alternatively (not shown) plural polar controlretarders may be provided on the input and output sides of the spatiallight modulator 48.

Polar control retarder 300 is arranged between the display polariser 218and the additional polariser 318, the at least one polar controlretarder 300 including a switchable liquid crystal retarder 301comprising a layer 214 of liquid crystal material. Polar controlretarders 300 comprise: (i) a switchable liquid crystal retarder 301comprising a layer 314 of liquid crystal material arranged betweentransparent support substrates 312, 316 and arranged between the displaypolariser 218 and the additional polariser 318; and (ii) at least onepassive compensation retarder 330.

FIG. 1A further illustrates a reflective polariser 302 that is arrangedbetween the output polariser 218 and the polar control retarder 300. Theoperation of polar control retarders 300 arranged between polariser 218,302, 318 will be described hereinbelow with respect to FIG. 22A to FIG.23D.

The display further comprises a control system arranged to independentlycontrol the at least one first light source 15 arrayed across an inputend of the waveguide 1 and the at least one second light source 17arrayed across an input end of the waveguide 1. The light sources 15, 17are arranged to provide input light to a waveguide 1.

Control of the polar control retarders is achieved by means of driver350 to change the operating voltage across the liquid crystal layer 314.Controller 352 is provided to control the driver 350 and controller 354that further controls the driving of light sources 15, 17.

The display device 100 is arranged to display an image and capable ofoperating in at least a public mode and a privacy mode, wherein in theprivacy mode the privacy function is provided and the visibility of theimage to an off-axis viewer is reduced compared to the public mode andthe visibility of the image to the primary user in an on-axis positionremains visible in both the privacy and public modes. The control system350, 352, 354 selectively operates the display device 100 in the publicmode or the privacy mode for at least one region of the displayed image,typically the entire displayed image. Such display device may be used inapplications such as but not limited to switchable privacy displays suchas laptops, monitors, TV, cell phone, tablets, wearable displays, ATMdisplays and automotive displays.

FIG. 1C is a schematic diagram illustrating a top view of a vehicle 650having the display apparatus 100 of FIG. 1A mounted therein. Occupantsmay include a passenger 45 and driver 47. It may be desirable thatdisplay 100 is operated as a privacy display for the passenger 45 thatis invisible to the driver 47 across the width of the display 100. Thuslight rays 447L, 447C, 447R from across the width of the displaydesirably have uniformly high security factor, S. Further it isdesirable that the passenger 45 sees an image with high luminance andimage visibility uniformity such that rays 445L, 445C, 445R provide animage with substantially uniform and high luminance.

FIG. 1D is a schematic diagram illustrating atop view of a vehiclehaving the display apparatus of FIG. 1A mounted therein for use by botha passenger 45 and a driver 47. The operation of the display 100 of FIG.1D is similar to that of FIG. 1C, other than the output light isdirected either side of the optical axis 199 of the display 100 toachieve efficient illumination of the driver 47 and passenger 45 withhigh image uniformity.

It may be desirable to provide a high efficiency display with highuniformity of luminance.

FIG. 2 is a schematic diagram illustrating a front perspective view of ahigh efficiency pupillated display 100. Features of the embodiment ofFIG. 2 not discussed in further detail may be assumed to correspond tothe features with equivalent reference numerals as discussed above,including any potential variations in the features. In comparison to thearrangement of FIG. 1A, polar control retarder 300 and additionalpolariser 318 is omitted. Such a display does not provide desirableimage security to off-axis snoopers. Collimation from waveguide 1desirably achieves light cones 415 with high luminance over a restrictedsolid angle to on-axis users and low brightness to off-axis locations atwhich viewers are not typically located. In an illustrative example,light cones 415 may have a full width half maximum angular size of lessthan 25° and more preferably less than 20°.

FIG. 2 further illustrates that light sources 17 may be omitted. Thepresent embodiments achieve increased uniformity for non-privacydisplays while providing high efficiency as will be described.

It would be desirable that light cones 415C, 415L, 415R, 415U, 415D areeach directed to a common direction.

The structure of an exemplary waveguide will now be described.

FIG. 3 is a schematic diagram illustrating a front perspective view of awaveguide 1 for use in a pupillated display 100.

Waveguide 1 is an optical waveguide that extends across a plane (x-yplane in FIG. 1A and FIG. 2 ) that comprises first and second opposedlight guiding surfaces 6,8 arranged to guide light rays 415, 406 alongthe waveguide 1. In the embodiments of the present description, the x,y, z directions are provided as an illustrative coordinate system, othercoordinate systems may be used as alternatives.

The first and second light guiding surfaces 6, 8 are arranged to guidelight by total internal reflection. In the embodiment of FIG. 3 , thesurface 6 comprises prismatic optical surfaces comprising first gentlysloped facets 32 and second steeply sloped facets 36 and the surface 8comprises lenticular microstructures extending in the y-direction thatis orthogonal to the lateral direction.

Waveguide 1 comprises an input end 2 arranged between the first andsecond light guiding surfaces 6, 8 and extending in a lateral direction(along the x-axis) between the first and second light guiding surfaces6,8.

The at least one light source 15 comprises an array of light sources 15that are arrayed across the lateral direction (that is parallel to thex-axis in the present embodiment). At least one light source 15 isarranged to input light into the waveguide through the input end 2.Light source may comprise an array of light sources, such as an LEDarray.

The operation of an illumination apparatus 110 will now be described.

FIG. 4A is a schematic diagram illustrating a side view of a pupillatedbacklight 20 for a first light source 15; and FIG. 4B is a schematicdiagram illustrating a side view of operation of variable tilt facets 53of an optical turning film component 50 of a pupillated backlight 20 fora first light source 15. Features of the embodiment of FIGS. 4A-B notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

Illumination apparatus 110 comprises: a waveguide 1 extending across aplane (x-y plane) and comprising: first and second opposed light guidingsurfaces 6, 8 arranged to guide light along the optical waveguide 1.

The second light guiding surface 8 is arranged to guide light by totalinternal reflection.

An input end 2 is arranged between the first and second light guidingsurfaces 6, 8 and extending in a lateral direction between the first andsecond light guiding surfaces 6, 8.

At least one light source 15 arranged to input light into the waveguide1 through the input end 2, wherein the waveguide 1 is arranged to causelight from the light sources 15 to exit from the waveguide 1 through thesecond light guiding surface 8 by breaking total internal reflection.

The optical turning film component 50 comprises: an input surface 56arranged to receive the light exiting from the waveguide 1, the inputsurface 56 extending across the plane (x-y plane); and an output surface58 facing the input surface 56. The input surface 56 comprises: an arrayof prismatic elements 52, each comprising a pair of facets 53 defining aridge 54 therebetween. The output surface 58 is planar. For each pair offacets 53A, 53B, the first facet 53A has a normal n_(A) on the internalside of the input surface 56 that is inclined towards a first side 52 ofthe optical turning film 50 and a second facet 53B has a normal n_(B) onthe internal side of the input surface 56 that is inclined towards asecond side 53 of the optical turning film 50 opposite to from the firstend 52, the first facets 53A having respective facet angles α, definedbetween the normal to the facet 53A and a normal (z-direction) to theplane (x-y plane), that vary across the array so that the deflectionvaries in a direction that is orthogonal (y-direction) to an opticalaxis 199 normal to the plane (z-direction) and corresponds to adirection orthogonal (y-direction) to the lateral direction(x-direction).

Incident rays 415 on the surface 8 of waveguide 1 have angles ofincidence at the surface 8 that are less than the critical angle at thesaid surface 8. Light cone 415 is determined at least in part by thecollimation of the light rays 415 from light sources 15 that breaksinternal reflection at the surface 8.

Grazing output light rays 415G are output from the waveguide 1 with acone angle 415 and substantially uniform output angle across the plane(x-y plane) of the waveguide 1.

The prismatic elements 51 of the optical turning film component 50 arearranged to deflect the light 415G exiting the waveguide 1, thedeflection varying in at least one direction across the plane (x-yplane).

Near the upper edge of the display, light rays 415G are refracted byfacets 53BU with facet angle β_(U) and reflected by total internalreflection at facets 53AU with surface normal direction n_(AU) withfacet angle α_(U) such that output light ray 415U is directed towards awindow 26A at a window distance Z_(wA) from the illumination apparatus110. In at least one cross sectional plane (y-z plane in FIGS. 4A-B),the size of the window 26 in the window plane 197A is determined by theangular width of the light cone 415, that may be for example by the fullwidth half maximum luminance of the cone 415.

In the present disclosure optical window 26A refers to the directing oflight by illumination apparatus 110 from light sources such as sources15 to defined spatial regions in a window plane 197, that is at thewindow distance Z_(wA) from the illumination apparatus. The opticalwindow 26 may also be referred to as an optical pupil. An observationfrom a location within the optical window provides light rays withcommon or substantially common optical properties from across theillumination apparatus 110.

The use of the term optical window 26 in the present embodiments isdistinct and different from the use of the term window when used torefer to sheets or panes of glass or other transparent material such asplastics for use in house windows, car windows and windscreens, andother types of protective windows. Such sheets or panes do notcontribute to the creation of desirable viewing regions with improveduniformity as described herein.

Similarly near the centre of the display, light rays 415G are refractedby facets 53BC with facet angle β_(C) and reflected by total internalreflection at facets 53AC with surface normal direction n_(AC) withfacet angle α_(C) such that output light ray 415C is directed towards awindow 26A in the window plane 197A at a window distance Z_(wA) from theillumination apparatus 110.

Similarly near the lower edge of the display, light rays 415G arerefracted by facets 53BD with facet angle β_(D) and reflected by totalinternal reflection at facets 53AD with surface normal direction n_(AC)with facet angle α_(D) such that output light ray 415D is directedtowards a window 26A in the window plane 197A at a window distanceZ_(wA) from the illumination apparatus 110.

Facet angles α, β may vary continuously with location across the lengthof the optical turning film component. The deflected light rays 415U,415C, 415D are directed towards a common optical window 26A in front ofthe illumination apparatus 110.

The operation of the optical turning film component with ridges 54 thatare arranged as straight lines will now be further described.

FIG. 4C is a schematic diagram illustrating a rear perspective view oflight output from a pupillated linear optical turning film component 50comprising variable tilt facets 53 of FIGS. 4A-B. Features of theembodiment of FIG. 4C not discussed in further detail may be assumed tocorrespond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.

FIG. 4C illustrates that the ridges 54 extend along an array of linesacross the plane (x-y plane) in which the input surface 56 extends. Theoptical turning film component 50 has a rectangular shape across theplane (x-y plane) and the lateral direction is along a major or minoraxis of the rectangular shape.

Facet angles α, β of respective facets 53, defined between a normal tothe facet 53 and a normal (z-direction) to the plane (x-y plane), varyacross the array so that the deflection varies in a direction(y-direction) that is orthogonal to an optical axis 199 that is normalto the plane (x-y plane), the direction corresponding to a direction(y-direction) that is orthogonal to the lateral direction (x-direction).

The lines are straight and facet 53 angles of respective facets 53,defined between a normal to the facet 53 and a normal to the plane (x-yplane), vary across the array so that the deflection varies in adirection that is orthogonal to the optical axis 199 corresponding to adirection that is orthogonal to the lateral direction.

The lines of the array have an arithmetic mean tangential angleprojected on to the plane (x-y plane) of 0° from the lateral direction,that is the lines are parallel to the x-axis direction that is thelateral direction in the present embodiment.

Thus the rays 415G are directed by the optical turning film component 50towards the common window 26A. Light rays 415UL, 415CL, 415DL from theupper, central and lower parts of the left edge region of the opticalturning film are located to the window 26A at a location correspondingto the lateral location of the left edge region in the lateraldirection. Light rays 415UC, 415CC, 415DC from the upper, central andlower parts of the central region of the optical turning film arelocated to the window 26A at a location in the lateral corresponding tothe lateral location of the central region in the lateral direction.Light rays 415UR, 415CR, 415DR from the upper, central and lower partsof the right edge region of the optical turning film are located to thewindow 26A at a location in the lateral corresponding to the laterallocation of the right edge region in the lateral direction.

In the embodiment of FIG. 4C there is no deflection in the lateraldirection and the optical window 26A thus has an extent in the lateraldirection that is determined by the width of the optical turning filmcomponent 50 and by the size of the solid angle of the cone 415; and awidth that is determined by the size of the solid angle of the cone 415.The size of the optical window 26A in the window plane 197A may also becontrolled by means of diffusion such as diffusers in the optical stack5 of the display as illustrated in FIG. 1A.

The embodiment of FIG. 4C further illustrates that the common opticalwindow 26A is offset from an optical axis 199 that extends from thecentre of optical turning film component 50 normal to the plane (x-yplane). Thus the point 198 at which the optical axis 199 intersects thewindow plane 197A is offset by distance Z_(OA) from the point 196 atwhich the ray 415CC intersects the window plane 197A. As will bedescribed hereinbelow, off-axis illumination locations may be achievedwith increased uniformity across the illumination apparatus.

It may be desirable to provide an optical window with reduced extent inthe direction that is orthogonal to the lateral direction.

FIG. 5A is a schematic diagram illustrating a front perspective view ofoperation of facets 53 of a curved optical turning film component 50 ofa pupillated backlight 20 for light from a first light source 15; andFIG. 5B is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component 50 comprisinguniform tilt facets 53. Features of the embodiment of FIGS. 5A-B notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

FIGS. 5A-B illustrate an alternative embodiment to the arrangement ofFIGS. 4A-C. In comparison to the arrangement of FIG. 4C, the lines ofthe ridges 54 are curved across the plane (x-y plane) so that thedeflection varies in a direction (x-direction) that is orthogonal to anoptical axis 199 that is normal to the plane (x-y plane), the direction(x-direction) corresponding to the lateral direction (x-direction).

The curved facets have surface normal directions n_(AK), n_(AC), n_(AL)that vary across the width of the optical turning film 50, that is thesurface normal directions vary in the lateral direction along a ridgesuch that light rays 415G from the waveguide 1 are directed towards acommon window 26B in a window plane 197B at a distance Z_(WB) from theoptical turning film component 50 of the illumination apparatus 110.

The optical window 26B has a cone width defined by cone 415 in directionorthogonal to the lateral direction and an extent determined by the conewidth 415 and the height of the optical turning film component 50, andis thus orthogonal to the optical window 26A illustrated in FIG. 4C.

In the embodiment of FIG. 5B, the centre of the optical window 26B isillustrated as aligned with the centre of the illumination apparatus110, that is the common optical window 26 is aligned with an opticalaxis 199 that extends from the centre of optical turning film componentnormal to the plane (x-y plane). The offset Z_(OB) of the optical window26B is zero and the lines of the array have an arithmetic meantangential angle projected on to the plane (x-y plane) that is inclinedat of 0° from the lateral direction.

The orientation of the lines of the array is described by facet peak 54rotations γ where γ_(R) is rotation at the right side of the displayγ_(C) is the rotation in the centre and ye is the rotation at the leftedge. The arithmetic mean tangential angle projected on to the plane(x-y plane) is the average rotation γ across the lateral direction.

The lines of the array may alternatively have an arithmetic meantangential angle that is inclined at more than 0° from the lateraldirection. Such an arrangement achieves an offset Z_(OB) that isnon-zero. Advantageously the nominal window 26B location may be set foroff-axis illumination with desirable properties as will be describedfurther hereinbelow.

It may be desirable to provide a common optical window for all pointsacross the illumination apparatus 110.

FIG. 5C is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component 50 comprisingvariable tilt facets 53 with a common optical window across theillumination apparatus. Features of the embodiment of FIG. 5C notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

The facet surfaces 53 are provided to achieve operation for rays 415G asillustrated in both FIG. 4B and FIG. 5A. Facet 53 angles of respectivefacets 53, defined between a normal to the facet 53 and a normal(z-direction) to the plane (x-y plane), vary across the array so thatthe deflection further varies in a direction orthogonal to the opticalaxis 199, corresponding to a direction orthogonal to the lateraldirection, so that the deflected light is directed towards a further,common optical window 26AB in front of the illumination apparatus 110.

The first mentioned common optical window 26A and the further commonoptical window 26B are defined the same distance in front of theillumination apparatus 110, achieving common optical window 26AB.Advantageously increased uniformity of output is achieved across thewhole of the illumination apparatus 110 from observation locationswithin the optical window 26AB.

FIG. 5D is a schematic diagram illustrating a rear perspective view oflight output from a curved optical turning film component 50 comprisingvariable tilt facets 53 with first and second different optical windowdistances 197A, 197B.

The first mentioned common optical window 26A and the further commonoptical window 26B are defined at different distances Z_(WA), Z_(WB) infront of the illumination apparatus 110. Further as described above, theoffset Z_(OA) may be provided by facet 53 angle selection and offsetZ_(OB) may be achieved by selection of the arithmetic mean tangentialangle projected on to the plane (x-y plane) of the inclination of thelines formed by the ridges 54 of the array. Advantageously increaseduniformity may be achieved for two different nominal observationdistances and angular locations.

The operation of the illumination apparatus 110 in a backlight 20 of adisplay apparatus 100 will now be described. For the purposes of thepresent description the backlights 20 are further referred to aspupillated backlights, that is backlights that provide optical windows26.

FIG. 6A is a schematic diagram illustrating a side view of operation ofan optical turning film component 50 comprising variable tilt facets 53of a pupillated backlight 20.

Light source array 15 is arranged at the lower edge of the backlight andrays 415L, 415R are directed towards optical window 26A that has anextent in the lateral direction as described above. In typicaloperation, the window distance between the backlight 20 and the windowplane 197 is arranged to be greater than the typical observer location.

In an illustrative example, a laptop display of diagonal size 14 inchesis arranged with a window distance Z_(WA) of 700 mm, while the nominalobserver location is in plane 145 at a distance Z_(V) of 500 mm. Thewindow distance Z_(WA) may be arranged by design of waveguide 1 andfacets 53 to be at a nominal snooper distance which may for example be700 mm.

FIG. 6B is a schematic diagram illustrating a top view of operation of acurved optical turning film component 50 of a pupillated backlight 20.

The window 26B may be at substantially the same distance as the window26A illustrated in FIG. 6A, and as illustrated in FIG. 5C, so that theplanes 197A, 197B are coincident. The snooper 47 is typically offset inthe lateral direction.

As will be described further in an illustrative example below, thearrangement of FIGS. 6A-6B advantageously achieve increased luminanceuniformity across the backlight 20 for the primary user 45.

Desirably the nominal user 45 plane 145 is closer to the backlight 20than the window plane 197. In operation the user 45 sees an image thathas increased uniformity in comparison to unpupillated backlights (i.e.backlights which do not provide a common optical window 26, or in otherwords provide a common optical window at optical infinity). When theobserver moves to the right side of the display, the display maintainsincreased brightness on the right side of the display in comparison tothe left side. By way of comparison, if the nominal observer distanceZ_(V) is arranged to be greater than the window distance Z_(WA), Z_(WB)then as the observer moves to the right from the central optical axis199, the right side of the display becomes darker than the left side ofthe image. Such a variation with observer position is typicallyconsidered unnatural and undesirable.

Further, the snooper 47 is desirably arranged at or further than thewindow distance Z_(WA), Z_(WB). Such an arrangement provides increaseduniformity of security factor across the display area in comparison tounpupillated backlights.

In alternative embodiments the windows 26A, 26B may be at differentdistances from the backlight 20, such as illustrated in FIG. 5D.Advantageously increased uniformity across the display area may beachieved for an increased range of observer 45 locations. Furtherincreased security factor in privacy mode of operation may be achievedfor an increased range of snooper 47 locations.

Features of the embodiment of FIGS. 6A-B not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

An illustrative embodiment will now be described.

FIG. 7 is a schematic graph illustrating the polar variation ofluminance for an illustrative backlight 20 with light input at the firstend of the waveguide 1. The waveguide 1 is of the form illustrated inFIG. 3 , and further diffusers are arranged to provide a desirable fullwidth half maximum in the lateral direction, FWHMx of 40°. Such abacklight profile is desirable to achieve high visual security levels indisplays of FIG. 1A provided with switchable polar control retarders300, while achieving desirable image luminance for higher viewing angleswhen operated in share mode.

Polar region 65 represents the field of view of the border of a 14″laptop display viewed by a head-on observer at 500 mm and polar region67 represents the field of view of the border of the display viewed byan off-axis snooper at 45 degrees and a distance along the normal 199 of600 mm.

In prior art unpupillated displays, the luminance contours vary acrossthe field of view. Thus a prior art display with such an unpupillatedbacklight has a central luminance of 100% and less than 50% luminance inthe upper right and upper left corners. It would be desirable toincrease the luminance uniformity for such a backlight profile.

In an illustrative embodiment of the arrangements of FIGS. 6A-B facetridges 54 are arranged as in TABLE 1.

TABLE 1 αU 58.1° βU 52.5° αD 52.5° βD 58.1° γL +12.5° γC 0.0° γR −12.5°

In the present embodiments, facet angles of respective facets 53,defined between a normal to the facet 53 and a normal (z-direction) tothe plane (x-y plane) may be between 40° and 70° preferably between42.5° and 65°, and more preferably between 42.5° and 62.5° as will befurther described with reference to FIG. 17C hereinbelow.

Further a polar control retarder 300 is provided as illustrated in FIG.1A and in TABLE 2.

TABLE 2 LC layer Alignment 314 Additional passive Additional passivetype retardance retarder 330 type retarder 330 retardance Homogeneous750 nm Homogeneous Negative C-plate −440 nm

Image uniformity can be assessed by comparing variation of luminanceacross the display for the viewing positions in polar space 29A˜M asindicated.

FIG. 8A is an array of schematic graphs illustrating the variation ofluminance for different viewing angles in a display 100 of FIG. 1Acomprising a curved optical turning film component 50 with variable tiltfacets 53; and by way of comparison with the present embodiments FIG. 8Bis an array of schematic graphs illustrating the variation of luminancefor different viewing angles in a display 100 comprising a linearoptical turning film component 50 with uniform tilt facets 53 such thatthe output is unpupillated.

Comparing FIG. 8A and FIG. 8B, for each viewing angle location, theuniformity of the display 100 across the area of the display isadvantageously increased. Further, the head-on luminance is not reducedand high power efficiency is achieved with low thickness.

The operation of the display in privacy mode to an observer 45 andsnooper 47 will now be described.

FIG. 9A is a schematic graph illustrating the polar variation oftransmission of a switchable retarder 300 arranged between parallelpolarisers 218, 318 for the switchable liquid crystal retarders 301driven for privacy mode; and FIG. 9B is a schematic graph illustratingthe polar variation of relative reflection of a switchable retarder 300arranged between a reflective polariser 302 and absorbing polariser 318for switchable liquid crystal retarders 301 of TABLE 2 driven in privacymode.

FIG. 9C is a schematic graph illustrating the polar and azimuthalvariation of visual security factor, S in the switchable privacy display100 of FIG. 1A and TABLE 2 driven in privacy mode of operation for adisplay 100 head-on luminance, of value Y_(max) measured in nits that ishalf of the illuminance of value I measured in lux. The backlight 20comprises the waveguide of FIG. 3 and the optical turning film componentof TABLE 1.

The variation of uniformity of security factor S with viewing locationwill now be described.

FIG. 10A is an array of schematic graphs illustrating the variation ofsecurity factor, S for different viewing angles in a display 100 of FIG.1A comprising a curved optical turning film component 50 with variabletilt facets 53 for a display 100 head-on luminance, of value Y_(max)measured in nits that is half of the illuminance of value I measured inlux. The viewer and snooper viewing distance is set to be 500 mm. Inpractice snoopers will be further from the display than the viewer andincreased security factor may be achieved.

By way of comparison FIG. 10B is an array of schematic graphsillustrating the variation of security factor, S for different viewingangles in a display 100 comprising a linear optical turning filmcomponent 50 with uniform tilt facets 53 for a display 100 head-onluminance, of value Y_(max) measured in nits that is half of theilluminance of value I measured in lux, that is for an unpupillatedbacklight 20. The viewer and snooper viewing distance is set to be 500mm.

In the graphs of FIGS. 9C-10B, regions with S<0.1 represent regions ofthe display with high image visibility, 0.1≤S<1.0 represent regions withreduced image visibility but are not private, 1.0≤S<1.8 representregions that are invisible depending on image content and S≥1.8represent regions where all images are substantially invisible.

Comparing FIGS. 10A and 10B advantageously the present embodiments (ofFIG. 10A) achieve increased image visibility for users near the axis.Further, for snoopers at higher angles such as at 40° increased imagesecurity is achieved across the whole of the display, that is thedisplay has switched to full privacy mode at a faster speed. Atintermediate angles, the security factor is more uniform across thedisplay area, advantageously achieving increased security performancefor all image data irrespective of location over the display activearea.

It would be desirable to provide a public mode of operation with higherluminance at off-axis positions.

FIG. 11A is a schematic diagram illustrating a side view of a pupillatedbacklight 20 for first and second light sources 15, 17; and FIG. 11B isa schematic diagram illustrating a side view of operation of variabletilt facets 53 of an optical turning film component 50 of a pupillatedbacklight 20 for first and second light sources 15, 17. Features of theembodiment of FIGS. 11A-B not discussed in further detail may be assumedto correspond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.

In comparison to the embodiments of FIGS. 4A-B, second light sources 17are arranged at the second end 4 of the waveguide 1 arranged to inputinput light in an opposite direction from the at least one firstmentioned light source, as further illustrated in FIG. 1A. In comparisonto the light leakage of FIG. 4 , light escapes the waveguide at least inpart by refraction at facets 36 of the waveguide 1 at which it isincident onto reflector 3, or may be directly incident onto opticalturning film component 50.

FIG. 1B illustrates that light rays 417G are output from the waveguide1, refract onto the facets 53B and then are directed by total internalreflection at facets 53A, that is in the opposite order to the lightrays 415G.

The deflected light through each input end 2, 4 is directed towards thesame common optical window 26 in front of the illumination apparatus110. As the deflection of the light rays 415, 417 is dominated by thereflection rather than the refraction, the present embodiments achievepupillation of light rays and provide optical windows 27A. Thus lightrays 417U, 415U may be directed in similar directions by means of facetangle selection γA, γB as described elsewhere herein.

FIG. 11C is a schematic graph illustrating the polar variation ofluminance for an illustrative backlight 20 with light input from lightsources 17 at the second end of the waveguide 1. The waveguide 1 is thusarranged to cause light from the at least one first light source 15 andthe at least one second light source 17 to exit from the waveguide 1with different angular distributions defined by light cone 427 incomparison to the narrow light cone 425 from light sources 15 and asillustrated in FIG. 4A. Advantageously increased luminance is providedin region 67 for off-axis users 47.

Such an arrangement can be used in a switchable privacy display furthercomprising polar control retarders 300 and polariser 318 of FIG. 1A. Thelight sources 15, 17 may be controlled in cooperation with theswitchable polar control retarder 300. In a first mode a privacy displaymay be provided with a small FWHMx and in a second mode a public modemay be provided with a larger FWHMx, and increased luminance at polarlocations that are greater the FWHM angles.

Alternatively such an arrangement can be used in a switchable highefficiency display of FIG. 2 and with further light sources 417 at thesecond end 4 of the waveguide 1. In a first mode a high efficiencydisplay may be provided with a small FWHMx and so reduced lateralviewing freedom with limited off-axis image visibility. In a second modea wider angle mode may be provided for enhanced off-axis imagevisibility.

The pupillation of FIG. 1I A desirably achieves increased imageuniformity from the variable tilt facets 53 of the optical turning filmcomponent 50 as described elsewhere herein.

The operation of the display backlight 20 for light rays 417G from thesecond end onto curved facets will now be described.

FIG. 12A is a schematic diagram illustrating a front perspective view ofoperation of facets 53 of a curved optical turning film component 50 ofa pupillated backlight 20 for light from first and second light sources15, 17; and FIG. 12B is a schematic diagram illustrating a top view ofoperation of a curved optical turning film component 50 of a pupillatedbacklight 20 for light from the second light source 17. Features of theembodiment of FIGS. 12A-B not discussed in further detail may be assumedto correspond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.

The lines of the ridges are curved so that the deflected light inputthrough the first end is directed towards a common optical window 27A infront of the illumination apparatus 110 and the deflected light inputthrough the second end 4 is directed towards a virtual common opticalwindow 27B behind the illumination apparatus 110, in the plane 197B.

Exemplary light rays 417CD, 417CC, 417CU illustrate that the backlight20 illuminates towards the user 45 and snooper 47, appearing tooriginate from the virtual optical window 27B. The luminance profile ofFIG. 11C is provided across the virtual window and desirable imageuniformity in the lateral direction may be advantageously achieved.

Alternative arrangements of operation of a display comprising differentoptical windows will now be described further.

FIG. 13A is a schematic diagram illustrating atop view of operation of alinear optical turning film component 50 of a pupillated backlight 20comprising variable tilt facets 53. Such an arrangement may be providedby the turning film component 50 of FIG. 4C for example. Advantageouslyfor light input from the second light source 17, increased uniformity isachieved in the lateral direction in comparison to the arrangement ofFIG. 12B while increased uniformity is achieved in the verticaldirection. Further the cost of tooling of the optical turning film andvisibility of Moiré artefacts that arise from curved lines of ridges 54may be reduced.

FIG. 13B is a schematic diagram illustrating a side view of operation ofa curved optical turning film component 50 of a pupillated backlight 20comprising uniform tilt facets 53. Such an arrangement may be providedby the turning film component 50 of FIG. 5B for example.

In comparison to the arrangement of FIG. 6A, the arrangement of FIG. 13Bmay provide increased lateral uniformity but conventional uniformityroll-off in the vertical direction.

Features of the embodiments of FIGS. 13A-B not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

FIG. 14 is a schematic diagram illustrating a rear perspective view of adiffused surface of an optical turning film component 50. The ridges 54and facets 53 comprise wobble. Advantageously display uniformity may beincreased. Visibility of artefacts arising from manufacturing defects ofwaveguide 1 may be reduced, advantageously increasing yield and reducingcost. Visibility of defects from damage in use of waveguide 1 may bereduced, advantageously increasing lifetime.

Alternative arrangements of waveguide 1 will now be described.

FIG. 15A is a schematic diagram illustrating a side view of a pupillatedbacklight 20 for first and second light sources 15, 17; and FIGS. 15B-Care schematic diagrams illustrating a front perspective view ofwaveguides 1 for use in a pupillated display 100. Features of theembodiments of FIGS. 15A-C not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

In comparison to the waveguide 1 of FIG. 3 , the waveguides 1 havemicrostructures arranged on a single surface that may be the firstsurface 6 or may be the second surface 8. In the alternative of FIG. 15Athe microstructures are arranged on the second surface 8 and light isoutput directly from the facets 36 onto the optical turning filmcomponent 50. The cone 417 for the second light sources 17 and cone 415for the first light sources 15 is pupillated as described elsewhereherein.

Advantageously the cost and complexity of the waveguides 1 may bereduced.

It may be desirable to provide first and second optical windows 26, 27that have the same or similar size.

FIG. 16A is a schematic diagram illustrating a side view of a pupillatedbacklight 20 for first and second light sources 15, 17; and FIGS. 16B-Care schematic diagrams illustrating a front perspective view ofwaveguides 1 for use in a pupillated display 100. Features of theembodiments of FIGS. 16A-C not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

In an alternative embodiment, the waveguide 1 is arranged to cause lightfrom the at least one first light source 15 and the at least one secondlight source 17 to exit from the waveguide 1 with a common angulardistribution, such that angular distributions 425, 427 are the same.

The waveguides 1 of FIGS. 16A-C are provided with first and secondfacets 32A, 32B rather than the facets 32, 36 described elsewhereherein. Facets 32A, 32B may have similar magnitude of angle of thesurface normal to the optical axis 199 direction, and are inclinedeither side of the optical axis. Output light cones 425, 427 fromrespective light sources 15, 17 have similar sizes and are arranged bymeans of the variable tilt of facets 53A, 53B in the directionorthogonal to the lateral direction to point to respective offsetoptical windows 26A, 26B.

FIG. 16A further illustrates that the location of first and secondoptical windows 26A, 26B from light sources 415, 417 respectively may beoffset from the optical axis 199 from the centre of the display, as alsoillustrated in FIG. 4C. Such an arrangement may provide offset viewinggeometries, as will be described with reference to FIG. 16D, below.

The optical windows 26A, 26B may be arranged in the same location thatmay be an on-axis location (centred around optical axis 199) or anoff-axis location. The control system is arranged to provideillumination from both the at least one first light source 15 and the atleast one second light source 17 so as to increase spatial uniformity ofillumination across the illumination device for at least one viewinglocation. In such an arrangement, the outputs from both waveguides 1 arecombined by the optical turning film component 50. Waveguides 1 may havenon-uniformities of extraction in the direction orthogonal to thelateral direction, that is dependent on distance from the light source15, so that such a combination may achieve improved extractionefficiency. Advantageously uniformity of luminance may be increased.

FIG. 16D is a schematic graph illustrating the polar variation ofluminance for the illustrative backlight 20 of FIGS. 16A-B with lightinput into the upper waveguide 1 from second light source 17.

Such an output may be suitable for application to a vehicle asillustrated in FIG. 1C, with fields of view 65, 67 for driver 45 andpassenger 47 respectively. The optical turning film is arranged toprovide optical windows 26A, 26B such that luminance uniformity isincreased.

Light input from the first light source 15 correspondingly produces asimilar high luminance profile in the region of the field of view 67 forthe passenger 47.

Such a backlight 20 may provide a display 100 that is visible to adriver at night-time, advantageously with low stray light to theremainder of the cabin. Further such a backlight 20 when illuminated bylight source 15 only may provide high luminance to the passenger 47 andnot to the driver. Such a backlight 20 may advantageously provide somedegree of image privacy to the driver 45. In another mode of operationboth light sources 15, 17 may be illuminated so that fields of view 65,67 may both be illuminated. Advantageously a high efficiency display 100may be provided.

It may be desirable to increase the uniformity of input light on to theoptical turning film 50.

FIG. 17A is a schematic diagram illustrating a side view of a pupillatedbacklight 20 comprising first and second waveguides 1A, 1B eachwaveguide 1A, 1B comprising a respective first light source 15A, 15B;and FIG. 17B is a schematic diagram illustrating a front perspectiveview of the pupillated backlight of FIG. 17A. Features of theembodiments of FIGS. 17A-B not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

In comparison to FIG. 1A, the illumination apparatus further comprisesat least one second light source 17 arranged to provide input light inan opposite direction from the at least one first mentioned light source15 as viewed along the optical axis 199 normal to the plane (x-y plane).The waveguide arrangement further comprises a second waveguide 1B thatextends across the same plane (x-y plane) as the first waveguide 1A andcomprises: first and second opposed light guiding surfaces 6A, 8Aarranged to guide light along the first waveguide 1A, the second lightguiding surface being arranged to guide light by total internalreflection; and an input end 2A arranged between the first and secondlight guiding surfaces 6A, 8A and extending in a lateral directionbetween the first and second light guiding surfaces 6A, 8A. The secondwaveguide 1B is arranged to receive the input light from the at leastone second light source 15B through the input end 2B, and being arrangedto cause light from the at least one second light source 15B to exitfrom the second waveguide 2B through the second light guiding surface bybreaking total internal reflection. The input surface of the opticalturning film component 50 is arranged to receive the light exiting fromthe first waveguide 1A and the second waveguide 1B.

The optical turning film component 50 comprises: an input surface 56arranged to receive the light exiting from the waveguide 1, the inputsurface 56 extending across the plane (x-y plane); and an output surface58 facing the input surface 56. The input surface 56 comprises: an arrayof prismatic elements 52 each comprising a pair of facets 53 defining aridge 54 therebetween. The output surface 58 is planar. For each pair offacets 53A, 53B, the first facet 53A has a normal n_(A) on the internalside of the input surface 56 that is inclined towards a first side 52 ofthe optical turning film 50 and a second facet 53B has a normal n_(B) onthe internal side of the input surface 56 that is inclined towards asecond side 53 of the optical turning film 50 opposite to from the firstend 52, the first facets 53A having respective facet angles α, definedbetween the normal to the facet 53A and a normal (z-direction) to theplane (x-y plane), that vary across the array so that the deflectionvaries in a direction that is orthogonal (y-direction) to an opticalaxis 199 normal to the plane (z-direction) and corresponds to adirection orthogonal (y-direction) to the lateral direction(x-direction).

In comparison to the embodiment of FIG. 1A, FIGS. 17A-B illustrate analternative backlight 20 of the present embodiments comprising first andsecond waveguides 1A, 1B with light sources 15A, 15B arranged on theshort sides of the waveguides 1A, 1B and at facing ends of respectivewaveguides 1A, 1B.

Considering a viewing arrangement similar to that illustrated in FIG.1C, the light sources 15A aligned with the front waveguide 1A arearranged to illuminate the passenger 45 while light sources 15B whilelight sources 15B aligned with the rear waveguide 1B are arranged toilluminate the driver 47. In operation, light rays 415A with cones 425Aare directed to a first optical window 26A, such as near to thepassenger 45 while light rays 415B with cones 425B are directed inparallel directions, that are towards the driver 47.

FIG. 17C is a schematic graph illustrating the variation of facet 53A,53B tilts a, 3 for various optical turning film components 50 of FIGS.17A-B for various illustrative embodiments.

FIG. 17A illustrates the angle α to the normal for the facet 53A forwhich light from light sources 15A is total internally reflected afterrefraction at facet 53B; and the angle f to the normal for the facet 53Bfor which light from light sources 15B is total internally reflectedafter refraction at facet 53A.

For a position x from one edge of the turning film component 50 of widthL, the relative position across the turning film component 50 is givenby x/L.

In a first illustrative embodiment of FIG. 17C, the facet angle α1varies with relative position x/L and the facet angle β1 is constant forall relative lateral positions, x/L. Light rays 415A are directedtowards a common window 26A that is near to optical axis.

Light rays 415B are directed towards a common window 26A that isinclined to optical axis 199 by refraction at facets 53A and totalinternal reflection at the facets 53B. The window distance Z_(wA) may beshorter than the window distance Z_(WB). For example the distance Z_(WA)may be near the passenger 45 nominal viewing distance while the distanceZ_(WB) may be at infinity. Advantageously the complexity of the toolingfor forming the prismatic array is reduced. Typically the distanceZ_(WA) is arranged to be greater than the nominal passenger distance toadvantageously achieve desirable luminance uniformity variations withlateral passenger 45 location.

Considering facets 53A, 53B at least some of the facets 53A haverespective facet angles α1, α2, defined between a normal to the facetand a normal (z-direction) to the plane (x-y plane), of between 52.5°and 62.5°. In respect of at least some of the facets 53B have respectivefacet angles β2, defined between a normal to the facet and a normal(z-direction) to the plane (x-y plane), of between 42.5° and 52.5°. Inanother embodiment at least some of the facets β1 have respective facetangle, defined between a normal to the facet and a normal (z-direction)to the plane (x-y plane), of between 40° and 52.5°.

In each pair of facets 53A, 53B, a first facet 53A has a normal on theinternal side of the input surface that is inclined towards the inputend 2 of the first waveguide 1A and a second facet 53B has a normal onthe internal side of the input surface that is inclined away from theinput end 2A of the first waveguide 1A, the first facets 53A havingrespective facet angles α, defined between the normal to the facet and anormal (z-direction) to the plane (x-y plane), that vary across thearray 50 so that the deflection varies in a direction that is orthogonalto an optical axis 199 normal (z-direction) to the plane (x-y plane) andcorresponds to a direction orthogonal to the lateral direction.

FIG. 17D is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide 1 ofFIG. 3 and the optical turning film component 50 of FIGS. 17A-C withfacet 53A, 53B angles α1, β1 for light from the first light source 15A;FIG. 17E is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide ofFIG. 3 and the optical turning film component 50 with facet 53A, 53Bangles α1, β1 of FIGS. 17A-C for light from the second light source 15B;and FIG. 17F is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide ofFIG. 3 and the optical turning film component 50 with facet 53A, 53Bangles α1, β1 of FIGS. 17A-C for light from the first and second lightsources 15A, 15B.

Referring to FIG. 17C, the first facets 53A have respective facet anglesα1, defined between a normal to the facet and a normal (z-direction) tothe plane (x-y plane), of between 52.5° and 62.5°. The second facets 53Bhave respective facet angles β1, defined between the normal to the facetand a normal (z-direction) to the plane (x-y plane), that are constantacross the array. Advantageously pupillation may be provided to a seconddisplay user, achieving increased uniformity and the cost of tooling ofthe surface may be reduced.

In an alternative arrangement, the first facets 53A have respectivefacet angles α2, defined between a normal to the facet and a normal(z-direction) to the plane (x-y plane), of between 52.5° and 62.5° andthe second facets 53B have respective facet angles β2, defined betweenthe normal to the facet and a normal (z-direction) to the plane (x-yplane), that vary across the array. The second facets 53B haverespective facet angles, defined between a normal to the facet and anormal (z-direction) to the plane (x-y plane), of between 40° and 52.5°.Advantageously pupillation may be provided to a second display user,achieving increased uniformity.

In an alternative embodiment, both the facet angles α2, β2 vary withrelative position x/L. Light rays 415A are directed towards a commonwindow 26A that is inclined around a 45° angle to optical axis 199 byrefraction at the facets 53B and total internal reflection at facets53A. Light rays 415B are directed by refraction at the facets 53A andtotal internal reflection at the facets 53B towards a common opticalwindow 26B that is near to optical axis 199.

The deflected light from each input end 2A, 2B is directed towardsrespective common optical windows 26A, 26B in front of the illuminationapparatus. The respective common optical windows 26A, 26B are indifferent locations in front of the illumination apparatus.

In alternative arrangements wherein the common optical windows 26A, 26Bare in the same location, increased brightness and uniformity may beachieved and for example switching between a narrow angle and wide anglemode of operation may advantageously be achieved.

In arrangements wherein the common optical windows are in differentlocations, different viewing locations may be provided, advantageouslywith increased brightness and uniformity.

Advantageously as both light rays 415A, 415B are directed to a commonoptical windows 26A, 26B by total internal reflection at facets 53A, 53Brespectively, pupillation may be achieved with similar window distancesZ_(WA), Z_(WB) compared to the embodiment of FIG. 17C which hasdifferent window distances.

A backlight 20 suitable for use in a switchable privacy display 100 ofthe type illustrated in FIG. 1C may be provided. A privacy mode to thepassenger 45 may be provided so the driver 47 cannot see the displayedimage by illumination of light source 15B. A low power mode to thepassenger 45 may be provided by illumination of light source 15B. A lowpower mode to the driver 47 may be provided by illumination of lightsource 15A. A sharing mode to the passenger 45 and driver 47 may beprovided by illumination of light sources 15A, 15B.

In an alternative embodiment of FIG. 17C, both the facet angles α3, β3vary with relative position x/L with facet angle α3 decreasing withrelative position and one facet angle 83 increasing with relativeposition x/L. Light rays 415A are directed towards a common window 26Athat is inclined with a large angle to optical axis 199 by refraction atthe facets 53B and total internal reflection at facets 53A. Light rays415B are directed by refraction at the facets 53A and total internalreflection at the facets 53B towards a common optical window 26B that isinclined to optical axis 199 with a large angle in the oppositedirection to the window 26A. Advantageously two off-axis optical windows26A, 26B may be achieved.

FIG. 17G is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide 1 ofFIG. 3 and the optical turning film component 50 of FIGS. 17A-C withfacet 53A, 53B angles α3, β3 for light from the first light source 15A;FIG. 17H is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide ofFIG. 3 and the optical turning film component 50 with facet 53A, 53Bangles α3, β3 of FIGS. 17A-C for light from the second light source 15B;and FIG. 17I is a schematic graph illustrating the polar variation ofluminance for the backlight 20 of FIG. 17A comprising the waveguide ofFIG. 3 and the optical turning film component 50 with facet 53A, 53Bangles α3, β3 of FIGS. 17A-C for light from the first and second lightsources 15A, 15B.

Referring to FIG. 17C the first facets 53A have respective facet anglesα3, defined between the normal to the facet and a normal (z-direction)to the plane (x-y plane), that increase across the array with distancex/L from the input end 2A of the first waveguide 1A, and the secondfacets 53B having respective facet angles 63, defined between the normalto the facet and a normal (z-direction) to the plane (x-y plane), thatdecrease across the array with distance x/L from the input end 2A of thefirst waveguide 1A. The first facets 53A have respective facet anglesα3, defined between a normal to the facet and a normal (z-direction) tothe plane (x-y plane), of between 42.5° and 52.5° and the second facets53B have respective facet angles β3, defined between a normal to thefacet and a normal (z-direction) to the plane (x-y plane), of between42.5° and 52.5°.

A backlight 20 suitable for use in a central automotive display 100 ofthe type illustrated in FIG. 1D may be provided. A low power mode to thepassenger 45 may be provided by illumination of light source 15B. A lowpower mode to the driver 47 may be provided by illumination of lightsource 15A. A sharing mode to the passenger 45 and driver 47 may beprovided by illumination of light sources 15A, 15B. Stray light in thevehicle 650 may be reduced to advantageously achieve increased safetyduring night-time driving and power efficiency is increased.

Embodiments of waveguide facets will now be described.

FIG. 18A is a schematic diagram illustrating a side view of part of apupillated backlight 20 comprising first and second waveguides 1A, 1B.Each waveguide 1A, 1B comprises gently sloped facets 32A, 32Brespectively and steeply sloped facets 36A, 36B. The surface normaldirection 37A of the facets 36A is not in the plane in which thewaveguide 1A extends. The axis 199 is orthogonal to the plane in whichthe waveguide 1A extends. The facet 36A has a surface normal direction37A that is inclined at an angle 39A to the axis 199, wherein the angle39A is less than 90 degrees.

In an illustrative embodiment the angle 39A may be 55 degrees. Moregenerally, the angle 39A may be at least 40 degrees and at most 70degrees, preferably may be at least 45 degrees and at most 65 degreesand more preferably may be at least 50 degrees and at most 60 degrees.

In operation, most light rays 415Ba from the waveguide 1B are refractedand pass through the waveguide 1A with a small deviation. However somelight rays 415Bb that are output from the waveguide 1B refract throughthe gently sloping facet 32A and are incident on the internal face ofthe steeply sloping facet 36A at which the light rays 415Bb undergototal internal reflection. The steeply sloping facet 36A has a surfacenormal direction 37A such that the totally internally reflected lightrays 415Bb are in the same or a similar direction to the light rays415Ba. Advantageously stray light is reduced and brightness isincreased.

By way of comparison with the alternative of FIG. 18A, FIG. 18B is aschematic diagram illustrating a side view of a pupillated backlight 20comprising first and second waveguides 1A, 1B wherein at least thewaveguide 1A comprises steeply sloped facets 36B with a surface normaldirection 37A that is in the plane in which the waveguide 1A extends.Thus the angle 39A between the axis 199 and surface normal direction 37Ais substantially 90 degrees.

In operation light rays 415Bb are reflected by total internal reflectionat the facet 36A and may be redirected within the waveguide 1A asillustrated. Such light rays 415Bb may provide increased stray light inundesirable polar directions that are different to the polar directionsfor light rays 415Ba. Luminance may be increased in undesirable polardirections, and security level of the display may be degraded.

Further light sources 17 may be provided.

FIG. 18C is a schematic diagram illustrating a side view of a pupillatedbacklight 20 comprising first and second waveguides 1A, 1B, eachwaveguide 1A, 1B comprising first and second light sources 15A, 17A and15B, 17B respectively. Features of the embodiments of FIGS. 18A-C notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

Light rays 415A with cones 425A are directed to a first optical window26A, such as near to a passenger 47 while light rays 415B with cones425B are directed to a second optical window 26B, such as near to adriver 45. Further light rays 417A with cones 427A are directed to thesecond optical window 26B, while light rays 417B with cones 427B aredirected to the first optical window 26A.

In comparison to the arrangement of FIG. 17A, the second light sources17A, 17B may provide a switchable wide angle output at locations ofdriver 45 and passenger 47 of FIG. 1C. Advantageously viewing freedom ofthe display may be increased when light sources 17A, 17B areilluminated.

The respective common optical windows 26A, 26B may be in the samelocation in front of the illumination apparatus. Advantageouslybrightness and uniformity may be increased.

It may be desirable to provide an optical window 26 with multipleluminance maxima.

FIG. 19A is a schematic diagram illustrating a side perspective view ofan optical turning film component 50 comprising first and second arraysof prismatic elements wherein the first array of prismatic elementscomprises curved prismatic elements 51; and FIG. 19B is a schematicgraph illustrating the polar variation of luminance for a backlight 20comprising the waveguide 1 of FIG. 3 and the optical turning filmcomponent 50 of FIG. 19A. Features of the embodiment of FIG. 19A notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

The lines of ridges 54A are curved in the plane of the optical turningfilm component 50 while the lines of the ridges 54B are linear in theplane. As illustrated in FIG. 19B, such a film may conveniently providedesirably high luminance in the region of an on-axis user 45 with fieldof view 65 in an on-axis location and a second user 47 in an off-axislocation with field of view 67. The pupillation of the curved ridges 54Aof the optical turning film component 50 may be arranged to provide anoptical window 26AB (such as illustrated in FIG. 5C) at or near theobserver 45 in such that the uniformity across the field of view 65 isadvantageously increased.

The pupillation of the linear ridges 54B may provide an extended window26B such that uniformity is increased for the observer 47 with field ofview 67.

In alternative embodiments both ridges 54A, 54B may have lines that arelinear in the plane. Advantageously visibility of Moiré may be reduced.

In alternative embodiments either or both ridges 54A, 54B may haveridges that are curved. Advantageously uniformity may be increased forboth users 45, 47.

In the embodiment and alternative embodiments of FIG. 19A,advantageously display efficiency and/or display luminance may beincreased for illumination of observers with typical viewing locations.The tilts of the ridges, or the arithmetic mean tangential angleprojected on to the plane for first and second ridges 54A, 54B may beadjusted to achieve location of maximum luminance and desirable observerlocations.

FIG. 19C is a schematic diagram illustrating a front perspective view ofa pupillated backlight comprising an optical turning film with a firstarray of prismatic elements that is linear and a second array ofprismatic elements that is curved. Features of the embodiment of FIG.19C not discussed in further detail may be assumed to correspond to thefeatures with equivalent reference numerals as discussed above,including any potential variations in the features.

In the alternative embodiment of FIG. 19C, the light sources 15B arearranged on the left-hand side of the waveguide 1B and the light sources15A are arranged on the lower side of the waveguide 1A.

In comparison to the light turning film component 50 of FIG. 19A, thepeaks 54B are orthogonal to the lateral direction. Such peak 54Bdirection provides facets that in operation behave in a similar manner(but not identically) to the turning film component 50 as illustrated inFIGS. 17B-C.

In comparison to the arrangement of FIG. 17B, the embodiment of FIG. 19Cmay advantageously achieve increased luminance to the user 45.

FIG. 19D is a schematic graph illustrating the polar variation ofluminance for the backlight of FIG. 19C comprising the waveguide of FIG.3 for light from the first light source 15A; FIG. 19E is a schematicgraph illustrating the polar variation of luminance for the backlight ofFIG. 19C comprising the waveguide of FIG. 3 for light from the secondlight source 15B; and FIG. 19F is a schematic graph illustrating thepolar variation of luminance for the backlight of FIG. 19C comprisingthe waveguide of FIG. 3 for light from the first and second lightsources 15A, 15B. Advantageously a backlight 20 suitable for use in aswitchable privacy display 100 of the type illustrated in FIG. 1C may beprovided. A privacy mode to the passenger 45 may be provided so thedriver 47 cannot see the displayed image by illumination of light source15B. A low power mode to the passenger 45 may be provided byillumination of light source 15B. A low power mode to the driver 47 maybe provided by illumination of light source 15A. A sharing mode to thepassenger 45 and driver 47 may be provided by illumination of lightsources 15A, 15B.

It may be desirable to provide different outputs for different regionsof a display.

FIG. 20 is a schematic diagram illustrating a top view of some elementsof a backlight 20 that is segmented. Features of the embodiment of FIG.20 not discussed in further detail may be assumed to correspond to thefeatures with equivalent reference numerals as discussed above,including any potential variations in the features.

First light source 15 comprises first and second parts 15A, 15B andsecond light source 17 comprises first and second parts 17A, 17B.Waveguide 1 may be of the type illustrated elsewhere herein, or may befirst and second waveguides 1A, 1B for example as illustrated in FIG.16B, in which case light sources 15AA, 15AB and light sources 15BA, 15BBare provided at respective ends of the waveguide.

Light rays 415A propagating within the waveguide 1 are input with anexpanding cone in the lateral direction. The microstructures on thesurfaces 6, 8 of the waveguide 1 adjust the ray 415A propagationdirections to achieve some collimation in the lateral direction and thusillumination regions 475A are provided with limited extent in thelateral direction. Such collimation can achieve partial illumination ofthe backlight in regions 475A that are determined by the location of thelight source along the first input end 2.

Similarly light rays 417B propagating within the waveguide 1 are inputwith an expanding cone in the lateral direction. Some collimation isprovided in the lateral direction and thus illumination regions 477B areprovided with limited extent in the lateral direction. Such collimationcan achieve partial illumination of the backlight in regions 477B thatare determined by the location of the light source along the input end4.

By control of light sources 15A, 15B and 17A, 17B, the directionality ofoutput may be different for different regions of the backlight 20. In anillustrative example, in one mode of operations, the left side of thedisplay 100 may be arranged for high image visibility to both users 45,47 and the right side of the display 100 may be provided for high imagesecurity factor to a snooper 47 with high image visibility to the user45. In other illustrative modes of operation, the whole display 100 maybe arranged to be seen by both users 45, 47 or the whole display 100 maybe arranged to be private to the user 45.

The number of light sources 15A-N may be adjusted to increase the numberof addressable regions of display control.

It may be desirable to provide a curved display.

FIG. 21 is a schematic diagram illustrating a top view of a curveddisplay 100 comprising a light pupillating optical turning filmcomponent 50. Features of the embodiment of FIG. 21 not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

In comparison to the embodiments described elsewhere herein, thebacklight 20C is curved. For comparison purposes the backlight 20F thatis the backlight 20C before curving is illustrated. The backlight 20F isprovided with a waveguide 1, and optical turning film component 50 thatis pupillated in at least one axis (by means of variable tilt facets 53,by means of curved ridges 54 or both) to provide an optical window 26Fin a window plane 197F as described elsewhere herein. After curving,backlight 20C provides a modified optical window 26C in a modifiedwindow plane 197C that is closer to the backlight than the opticalwindow 26F.

Advantageously the curvature of the display can be provided forcomfortable viewing by the user 45, and the optical window 26C can beprovided for desirable image uniformity and variation of uniformity withuser 45 location. Further in a privacy display, increased uniformity ofsecurity factor can be provided to off-axis snooper 47.

Operation of the switchable retarders of FIG. 1A and FIG. 1B will now bedescribed.

FIG. 22A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1A in a privacy mode of operation.

When the layer 314 of liquid crystal material 414 is driven to operatein the privacy mode, the retarders 300 provide no overall transformationof polarisation component 360 to output light rays 400 passingtherethrough along an axis perpendicular to the plane of the switchableretarder, but provides an overall transformation of polarisationcomponent 361 to light rays 415 passing therethrough for some polarangles which are at an acute angle to the perpendicular to the plane ofthe retarders.

Polarisation component 360 from the output polariser 218 is transmittedby reflective polariser 302 and incident on retarders 300. On-axis lighthas a polarisation component 362 that is unmodified from component 360while off-axis light has a polarisation component 364 that istransformed by the retarders 300. At a minimum, the polarisationcomponent 361 is transformed to a linear polarisation component 364 andabsorbed by additional polariser 318. More generally, the polarisationcomponent 361 is transformed to an elliptical polarisation component,that is partially absorbed by additional polariser 318.

The polar distribution of light transmission illustrated in FIG. 9Amodifies the polar distribution of luminance output of the underlyingspatial light modulator 48. In the case that the spatial light modulator48 comprises a directional backlight 20 then off-axis luminance may befurther be reduced as described above.

Features of the embodiment of FIG. 22A not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

Advantageously, a privacy display is provided that has low luminance toan off-axis snooper while maintaining high luminance for an on-axisobserver.

The operation of the reflective polariser 302 for light from ambientlight source 604 will now be described for the display operating inprivacy mode.

FIG. 22B is a schematic diagram illustrating in top view propagation ofambient illumination light through the optical stack of FIG. 1A in aprivacy mode of operation.

Ambient light source 604 illuminates the display device 100 withunpolarised light. Additional polariser 318 transmits light ray 410normal to the display device 100 with a first polarisation component 372that is a linear polarisation component parallel to the electric vectortransmission direction 319 of the additional polariser 318.

In both states of operation, the polarisation component 372 remainsunmodified by the retarders 300 and so transmitted polarisationcomponent 382 is parallel to the transmission axis of the reflectivepolariser 302 and the output polariser 218, so ambient light is directedthrough the spatial light modulator 48 and lost.

By comparison, for ray 412, off-axis light is directed through theretarders 300 such that polarisation component 374 incident on thereflective polariser 302 may be reflected. Such polarisation componentis re-converted into component 376 after passing through retarders 300and is transmitted through the additional polariser 318.

Thus when the layer 314 of liquid crystal material is in the secondstate of said two states, the reflective polariser 302 provides noreflected light for ambient light rays 410 passing through theadditional polariser 318 and then the retarders 300 along an axisperpendicular to the plane of the retarders 300, but provides reflectedlight rays 412 for ambient light passing through the additionalpolariser 318 and then the retarders 300 at some polar angles which areat an acute angle to the perpendicular to the plane of the retarders300; wherein the reflected light 412 passes back through the retarders300 and is then transmitted by the additional polariser 318.

The retarders 300 thus provide no overall transformation of polarisationcomponent 380 to ambient light rays 410 passing through the additionalpolariser 318 and then the retarder 300 along an axis perpendicular tothe plane of the switchable retarder, but provides an overalltransformation of polarisation component 372 to ambient light rays 412passing through the absorptive polariser 318 and then the retarders 300at some polar angles which are at an acute angle to the perpendicular tothe plane of the retarders 300.

The polar distribution of light reflection illustrated in FIG. 9B thusillustrates that high reflectivity can be provided at typical snooperlocations by means of the privacy state of the retarders 300. Thus, inthe privacy mode of operation, the reflectivity for off-axis viewingpositions is increased as illustrated in FIG. 9B, and the luminance foroff-axis light from the spatial light modulator is reduced asillustrated in FIG. 9A.

In the public mode of operation, the control system 710, 752, 350 isarranged to switch the switchable liquid crystal retarder 301 into asecond retarder state in which a phase shift is introduced topolarisation components of light passing therethrough along an axisinclined to a normal (z-direction) to the plane (x-y plane) of theswitchable liquid crystal retarder 301.

By way of comparison, solid angular extent 415D may be substantially thesame as solid angular extent 415B in a public mode of operation. Suchcontrol of output solid angular extents 415C, 415D may be achieved bysynchronous control of the sets 15, 17 of light sources and the at leastone switchable liquid crystal retarder 300.

Advantageously a privacy mode may be achieved with low image visibilityfor off-axis viewing and a large solid angular extent may be providedwith high efficiency for a public mode of operation, for sharing displayimagery between multiple users and increasing image spatial uniformity.

Additional polariser 318 is arranged on the same output side of thespatial light modulator 48 as the display output polariser 218 which maybe an absorbing dichroic polariser. The display polariser 218 and theadditional polariser 318 have electric vector transmission directions219, 319 that are parallel. As will be described below, such parallelalignment provides high transmission for central viewing locations.

A transmissive spatial light modulator 48 arranged to receive the outputlight from the backlight; an input polariser 210 arranged on the inputside of the spatial light modulator between the backlight 20 and thespatial light modulator 48, an output polariser 218 arranged on theoutput side of the spatial light modulator 48; an additional polariser318 arranged on the output side of the output polariser 218; and aswitchable liquid crystal retarder 300 comprising a layer 314 of liquidcrystal material arranged between the at least one additional polariser318 and the output polariser 218 in this case in which the additionalpolariser 318 is arranged on the output side of the output polariser218; and a control system 710 arranged to synchronously control thelight sources 15, 17 and the at least one switchable liquid crystalretarder 300.

Control system 710 further comprises control of voltage controller 752that is arranged to provide control of voltage driver 350, in order toachieve control of switchable liquid crystal retarder 301.

Features of the embodiment of FIG. 22B not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

Advantageously, a privacy display is provided that has high reflectivityto an off-axis snooper while maintaining low reflectivity for an on-axisobserver. As described above, such increased reflectivity providesenhanced privacy performance for the display in an ambiently illuminatedenvironment.

Operation in the public mode will now be described.

FIG. 23A is a schematic diagram illustrating in side view propagation ofoutput light from a spatial light modulator through the optical stack ofFIG. 1A in a public mode of operation; and FIG. 23B is a schematic graphillustrating the variation of output luminance with polar direction forthe transmitted light rays in FIG. 23A.

Features of the embodiment of FIG. 23A and FIG. 23B not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

When the liquid crystal retarder 301 is in a first state of said twostates, the polar control retarder 300 provides no overalltransformation of polarisation component 360, 361 to output lightpassing therethrough perpendicular to the plane of the switchableretarder 301 or at an acute angle to the perpendicular to the plane ofthe switchable retarder 301. That is polarisation component 362 issubstantially the same as polarisation component 360 and polarisationcomponent 364 is substantially the same as polarisation component 361.Thus the angular transmission profile of FIG. 23B is substantiallyuniformly transmitting across a wide polar region. Advantageously adisplay may be switched to a wide field of view.

FIG. 23C is a schematic diagram illustrating in top view propagation ofambient illumination light through the optical stack of FIG. 1A in apublic mode of operation; and FIG. 23D is a schematic graph illustratingthe variation of reflectivity with polar direction for the reflectedlight rays in FIG. 23C.

Thus when the liquid crystal retarder 301 is in the first state of saidtwo states, the retarders 300 provide no overall transformation ofpolarisation component 372 to ambient light rays 412 passing through theadditional polariser 318 and then the retarders 300, that isperpendicular to the plane of the retarders 300 or at an acute angle tothe perpendicular to the plane of the retarders 300.

In operation in the public mode, input light ray 412 has polarisationstate 372 after transmission through the additional polariser 318. Forboth head-on and off-axis directions no polarisation transformationoccurs and thus the reflectivity for light rays 415 from the reflectivepolariser 302 is low. Light ray 412 is transmitted by reflectivepolariser 302 and lost in the display polarisers 218, 210 or thebacklight of FIG. 1A.

Features of the embodiment of FIG. 23C and FIG. 23D not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

Advantageously in a public mode of operation, high luminance and lowreflectivity is provided across a wide field of view. Such a display canbe conveniently viewed with high contrast by multiple observers.

Other types of switchable privacy display will now be described.

A display device 100 that may be switched between privacy and publicmodes of operation comprises an imaging waveguide and an array of lightsources as described in U.S. Pat. No. 9,519,153, which is incorporatedby reference herein in its entirety. The imaging waveguide images anarray of light sources to optical windows that may be controlled toprovide high luminance on-axis and low luminance off-axis in a privacymode, and high luminance with a large solid angle cone for publicoperation.

As may be used herein, the terms “substantially” and “approximately”provide an industry-accepted tolerance for its corresponding term and/orrelativity between items. Such an industry-accepted tolerance rangesfrom zero percent to ten percent and corresponds to, but is not limitedto, component values, angles, et cetera. Such relativity between itemsranges between approximately zero percent to ten percent.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and not limitation. Thus, thebreadth and scope of this disclosure should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with any claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theembodiment(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” the claims should not be limited by the languagechosen under this heading to describe the so-called field. Further, adescription of a technology in the “Background” is not to be construedas an admission that certain technology is prior art to anyembodiment(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the embodiment(s) set forth inissued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple embodimentsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theembodiment(s), and their equivalents, that are protected thereby. In allinstances, the scope of such claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

1. An illumination apparatus comprising: at least one light sourcearranged to provide input light; a waveguide arrangement comprising atleast a first waveguide that extends across a plane and comprises: firstand second opposed light guiding surfaces arranged to guide light alongthe first waveguide, the second light guiding surface being arranged toguide light by total internal reflection; and an input end arrangedbetween the first and second light guiding surfaces and extending in alateral direction between the first and second light guiding surfaces,the first waveguide being arranged to receive the input light from theat least one light source through the input end, and being arranged tocause light from the at least one light source to exit from the firstwaveguide through the second light guiding surface by breaking totalinternal reflection; and an optical turning film component comprising:an input surface arranged to receive the light exiting from the firstwaveguide, the input surface extending across the plane; and an outputsurface facing the input surface, wherein the input surface comprises:an array of prismatic elements each comprising a pair of facets defininga ridge therebetween, the ridges extending along an array of linesacross the plane in which the input surface extends, wherein theprismatic elements are arranged to deflect the light exiting the firstwaveguide, the deflection varying in at least one direction across theplane so that the deflected light is directed from a virtual commonoptical window behind the illumination apparatus.
 2. An illuminationapparatus according to claim 1, wherein the lines are curved across theplane so that the deflection varies in a direction that is orthogonal toan optical axis normal to the plane and corresponds to the lateraldirection. 3-5. (canceled)
 6. An illumination apparatus according toclaim 1, wherein the facets have respective facet angles, definedbetween a normal to the facet and a normal to the plane, that varyacross the array so that the deflection varies in a direction that isorthogonal to an optical axis normal to the plane and corresponds to adirection orthogonal to the lateral direction.
 7. An illuminationapparatus according to claim 1, wherein the lines of the array have anarithmetic mean tangential angle projected on to the plane of 0° fromthe lateral direction.
 8. An illumination apparatus according to claim1, wherein the lines of the array have an arithmetic mean tangentialangle projected on to the plane that is inclined at more than 0° fromthe lateral direction.
 9. An illumination apparatus according to claim1, wherein the optical turning film component has a rectangular shapeacross the plane and the lateral direction is along a major or minoraxis of the rectangular shape.
 10. An illumination apparatus accordingto claim 1, wherein the output surface is planar.
 11. An illuminationapparatus according to claim 1, wherein the facets have respective facetangles, defined between a normal to the facet and a normal to the plane,of between 40° and 70°, preferably between 42.5° and 65°, and morepreferably between 42.5° and 62.5°.
 12. An illumination apparatusaccording to claim 1, wherein at least some of the facets haverespective facet angles, defined between a normal to the facet and anormal to the plane, of between 52.5° and 62.5°.
 13. An illuminationapparatus according to claim 1, wherein in respect of at least some ofthe facets have respective facet angles, defined between a normal to thefacet and a normal to the plane, of between 42.5° and 52.5°.
 14. Anillumination apparatus according to claim 1, wherein at least some ofthe facets have respective facet angle, defined between a normal to thefacet and a normal to the plane, of between 40° and 52.5°.
 15. Anillumination apparatus according to claim 1, wherein in each pair offacets, a first facet has a normal on the internal side of the inputsurface that is inclined towards the input end of the first waveguideand a second facet has a normal on the internal side of the inputsurface that is inclined away from the input end of the first waveguide,the first facets having respective facet angles, defined between thenormal to the facet and a normal to the plane, that vary across thearray so that the deflection varies in a direction that is orthogonal toan optical axis normal to the plane and corresponds to a directionorthogonal to the lateral direction.
 16. An illumination apparatusaccording to claim 15, wherein the first facets have respective facetangles, defined between a normal to the facet and a normal to the plane,of between 52.5° and 62.5°.
 17. An illumination apparatus according toclaim 15, wherein the second facets have respective facet angles,defined between the normal to the facet and a normal to the plane, thatare constant across the array.
 18. An illumination apparatus accordingto claim 15, wherein the second facets have respective facet angles,defined between the normal to the facet and a normal to the plane, thatvary across the array.
 19. An illumination apparatus according to claim15, wherein the second facets have respective facet angles, definedbetween a normal to the facet and a normal to the plane, of between 40°and 52.5°.
 20. An illumination apparatus according to claim 15, whereinthe first facets have respective facet angles, defined between thenormal to the facet and a normal to the plane, that increase across thearray with distance from the input end, and the second facets havingrespective facet angles, defined between the normal to the facet and anormal to the plane, that decrease across the array with distance fromthe input end.
 21. An illumination apparatus according to claim 20,wherein the first facets have respective facet angles, defined between anormal to the facet and a normal to the plane, of between 42.5° and52.5° and the second facets have respective facet angles, definedbetween a normal to the facet and a normal to the plane, of between42.5° and 52.5°.
 22. An illumination apparatus according to claim 1,wherein the at least one light source comprises an array of lightsources arrayed across the input end.
 23. An illumination apparatusaccording to claim 1, wherein the common optical window is aligned withan optical axis that extends from the centre of the optical turning filmcomponent normal to the plane.
 24. An illumination apparatus accordingto claim 1, wherein the common optical window is offset from an opticalaxis that extends from the centre of the optical turning film componentnormal to the plane.
 25. An illumination apparatus according to claim 1,wherein the first waveguide further comprises a second input endarranged between the first and second light guiding surfaces opposite tothe first mentioned input end, and the illumination apparatus furthercomprises at least one second light source arranged to input light intothe waveguide through the second input end in an opposite direction fromthe at least one first mentioned light source. 26-30. (canceled)
 31. Anillumination apparatus according to claim 25, further comprising acontrol system arranged to control the at least one first light sourceand the at least one second light source independently.
 32. Anillumination apparatus according to claim 31, wherein in one mode ofoperation the control system is arranged to provide illumination fromboth the at least one first light source and the at least one secondlight sources so as to increase spatial uniformity of illuminationacross the illumination device for at least one viewing location.
 33. Anillumination apparatus according to claim 25, wherein the waveguide isarranged to cause light from the at least one first light source and theat least one second light source to exit from the waveguide withdifferent angular distributions.
 34. An illumination apparatus accordingto claim 25, wherein the waveguide is arranged to cause light from theat least one first light source and the at least one second light sourceto exit from the waveguide with a common angular distribution.
 35. Abacklight apparatus comprising: an illumination apparatus according toclaim 1; and a rear reflector arranged to receive light exiting from thefirst surface of waveguide and direct it back through the waveguide. 36.A display apparatus comprising: a backlight apparatus according to claim35; and a spatial light modulator arranged to receive light from thebacklight apparatus.
 37. A display apparatus according to claim 36,further comprising: at least one display polariser arranged on a side ofthe spatial light modulator; an additional polariser arranged on thesame side of the spatial light modulator as the display polariser; andat least one polar control retarder arranged between the displaypolariser and the additional polariser, the at least one polar controlretarder including a switchable liquid crystal retarder comprising alayer of liquid crystal material.
 38. A vehicle having a displayapparatus according to claim 37 mounted therein.
 39. An optical turningfilm component comprising: an input surface for receiving light exitingfrom a waveguide through a light guiding surface of the waveguide bybreaking total internal reflection, the input surface extending across aplane; and an output surface facing the input surface, wherein the inputsurface comprises: an array of prismatic elements each comprising a pairof facets defining a ridge therebetween, the ridges extending along anarray of lines across the plane in which the input surface extends,wherein the prismatic elements are arranged to deflect the light exitingthe waveguide, the deflection varying in at least one direction acrossthe plane so that the deflected light is directed from a virtual commonoptical window behind the illumination apparatus.
 40. An optical turningfilm component according to claim 39, wherein the lines are curvedacross the plane so that the deflection varies in a direction orthogonalto an optical axis that is normal to the plane and corresponds to thelateral direction.
 41. (canceled)
 42. An optical turning film componentaccording to claim 39, wherein the facets have respective facet angles,defined between a normal to the facet and a normal to the plane, thatvary across the array so that the deflection varies in a direction thatis orthogonal to an optical axis normal to the plane and corresponds toa direction orthogonal to the lateral direction.
 43. An optical turningfilm component according to claim 39, wherein the lines of the arrayhave an arithmetic mean tangential angle projected on to the plane of 0°from the lateral direction.
 44. An optical turning film componentaccording to claim 39, wherein the lines of the array have an arithmeticmean tangential angle projected on to the plane that is inclined at morethan 0° from the lateral direction.
 45. An optical turning filmcomponent according to claim 39, wherein the optical turning filmcomponent has a rectangular shape across the plane and the lateraldirection is along a major or minor axis of the rectangular shape. 46.An optical turning film component according to claim 39, wherein theoutput surface is planar.
 47. An optical turning film componentaccording to claim 39, wherein the facets have respective facet angles,defined between a normal to the facet and a normal to the plane, ofbetween 40° and 70°, preferably between 42.5° and 65°, and morepreferably between 42.5° and 62.5°.
 48. An optical turning filmcomponent according to claim 39, wherein at least some of the facetshave respective facet angles, defined between a normal to the facet anda normal to the plane, of between 52.5° and 62.5°.
 49. An opticalturning film component according to claim 39, wherein at least some ofthe facets have respective facet angles, defined between a normal to thefacet and a normal to the plane, of between 42.5° and 52.5°.
 50. Anoptical turning film component according to claim 39, wherein at leastsome of the facets have respective facet angles, defined between anormal to the facet and a normal to the plane, of between 40° and 52.5°.51. An optical turning film component according to claim 39, wherein ineach pair of facets, a first facet has a normal on the internal side ofthe input surface that is inclined towards a first side of the opticalturning film and a second facet has a normal on the internal side of theinput surface that is inclined towards a second side of the opticalturning film opposite to the first end, the first facets havingrespective facet angles, defined between the normal to the facet and anormal to the plane, that vary across the array so that the deflectionvaries in a direction that is orthogonal to an optical axis normal tothe plane and corresponds to a direction orthogonal to the lateraldirection.
 52. An optical turning film component according to claim 51,wherein the first facets have respective facet angles, defined between anormal to the facet and a normal to the plane, of between 52.5° and62.5°.
 53. An optical turning film component according to claim 51,wherein the second facets have respective facet angles, defined betweenthe normal to the facet and a normal to the plane, that are constantacross the array.
 54. An optical turning film component according toclaim 51, wherein the second facets have respective facet angles,defined between the normal to the facet and a normal to the plane, thatvary across the array.
 55. An optical turning film component accordingto claim 51, wherein the second facets have respective facet angles,defined between a normal to the facet and a normal to the plane, ofbetween 40° and 52.5°.
 56. An optical turning film component accordingto claim 51, wherein the first facets have respective facet angles,defined between the normal to the facet and a normal to the plane, thatincrease across the array in a direction from the first side to thesecond side, and the second facets having respective facet angles,defined between the normal to the facet and a normal to the plane, thatdecrease across the array in direction from the first side to the secondside.
 57. An optical turning film component according to claim 56,wherein the first facets have respective facet angles, defined between anormal to the facet and a normal to the plane, of between 42.5° and52.5° and the second facets have respective facet angles, definedbetween a normal to the facet and a normal to the plane, of between42.5° and 52.5°.
 58. An optical turning film component according toclaim 39, wherein the common optical window is aligned with an opticalaxis that extends from the centre of optical turning film componentnormal to the plane.
 59. An optical turning film component according toclaim 39, wherein the common optical window is offset from an opticalaxis that extends from the centre of optical turning film componentnormal to the plane.
 60. An optical turning film component according toclaim 39, wherein the lines are straight and facet angles of respectivefacets, defined between a normal to the facet and a normal to the plane,vary across the array so that the deflection varies in a directionorthogonal to the optical axis corresponding to a direction orthogonalto the lateral direction.
 61. (canceled)